Metallocorroles

ABSTRACT

Metallocorrole complexes of third row transition metals (see Formula I below) may be used as therapeutic agents, catalysts, components of oxygen detectors, and components of light emitting diodes. In particular, metallocorrole complexes of third row transition metals may be used as improved photosenitizers in photodynamic therapy; as improved catalysts in aziridination, epoxidation, and water splitting reactions; as improved in vivo imaging agents; and as improved components in the emissive layer of OLEDs. Due to their strongly sigma-donating nature, corroles are able to stabilize third row transition metals in high oxidation states. Third row transition metals are significantly more electropositive than their first and second row counterparts and may therefore act as improved catalysts. In addition, the high spin-orbit coupling constants of third row transition metals may lead to easier singlet-triplet inter-system crossing in the excited state, which in turn may allow for long-wavelength phosphorescence that is desirable for many applications.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of U.S. ProvisionalApplication Ser. No. 61/180,749, filed on May 22, 2009, and titled“High-T Luminescent Metallocorroles,” the entire content of which isincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has certain rights in this invention pursuant toGrant No. CHE0518164 awarded by the National Science Foundation.

FIELD

The present invention relates generally to metallocorrole compoundscontaining a third row transition metal.

BACKGROUND

Metalloporphyrin complexes that phosphoresce at ambient temperatureshave been used widely in photodynamic therapy (PDT), oxygen detection,and organic light emitting diodes (OLEDs). The most commonly usedmetalloporphyrins are d⁸ [primarily platinum(II), palladium(II), andgold(III)] and lanthanide complexes that emit at relatively longwavelengths (>600 nm) with lifetimes, in solution, in the 10-50 μs rangeunder anaerobic conditions at room temperature. Although d⁶metalloporphyrins are known to have desirable photophysical properties,they have found limited application. For example, ruthenium(II)porphyrins phosphoresce at room temperature at wavelengths longer thanthose of platinum(II) analogues, but have been less commonly used, dueto oxidative instabilities. Porphyrin ligands are limited, however, intheir emission intensity and their ability to stabilize metals in highoxidation states.

While metalloporphyrin complexes have been widely used, they typicallystabilize metals in lower oxidation states than do corroles.Accordingly, first and second row transition metal corrole complexeshave been investigated in an attempt to discover compounds capable ofstabilizing metals in higher oxidation states. These corrole ligands aremore electron-rich, and their strong sigma-donating nature enables themto stabilize high-valent metal centers that porphyrins cannot. Highermetal oxidation states strongly affect the redox properties of thechelated metal ion, and certain high-valent metal centers are desirablefor catalysis. Additionally, corrole complexes produce more intenseemission than metalloporphyrins.

These first and second row transition metal corrole complexes are,however, typically limited to fluorescence emission. In addition totheir therapeutic uses, first row transition metal corroles function asgood catalysts. For example, such corroles can be used in the activationof O₂ by trivalent chromium, manganese, and iron; catalytic reduction ofCO₂ by iron(I) and cobalt(I); and iron(IV) aziridination of olefins. Theredox processes of first and second row transition metal corrolecomplexes are, however, more often ligand-centered than metal-centered.

SUMMARY

Embodiments of the present invention relate to metallocorrolesrepresented by Formula I:

In Formula I, M is selected from third row transition metals. Each of R₁through R₃ is independently selected aryl groups and heteroaryl groups.Each of X₁ through X₈ is independently H, halides, aldehydes, carboxylicacids, cyanoacetates, sulfonyls, SO₂Cl, SO₃H, SO₂NR₁R₂, CO₂H, COCl,CONR₄R₅, CHO or NO₂, wherein R₄ and R₅ may be the same or different, andeach is selected from H, alkyl, aryl, and heteroaryl; and each of L₁ andL₂ is a binding site or an axial ligand.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the office upon request and paymentof the necessary fee.

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the attached drawings, in which:

FIG. 1 is a graph of emission (phosphorescence) spectra of 1-tma and2-tma, in CH₂Cl₂ solutions at room temperature.

FIG. 2 is a graph of emission (phosphorescence) spectra of 1-py and1-CNpy, in CH₂Cl₂ solutions at room temperature.

FIG. 3 is a graph of a ¹H nuclear magnetic resonance (NMR) spectrum of 1in CD₂Cl₂ and UV-vis spectra of 1 (red) and 2 (blue) in CH₂Cl₂; inset isa graph of the β-pyrrole proton resonances.

FIG. 4 is a graph of cyclic voltammogram (CV) traces of 1-Ir(tma)₂ (inred) and 2-Ir(tma)₂ (in blue) in CH₂Cl₂ solution at 23° C.

FIG. 5 is an illustration of the X-ray structures of 1 (left) and 2(right), illustrating: 50% probability displacement ellipsoids; andaverage bond distances of: Ir—N (equatorial) 1.965 (9) [1-Ir(tma)₂],1.974(3) [2-Ir(tma)₂] and Ir—N (axial) 2.185 (9) [1-Ir(tma)₂], 2.189(3)[2-Ir(tma)₂].

FIG. 6 is a graph of emission spectra of Ir(III) corroles in degassedtoluene solution (λ_(ex)=0.496.5 nm); a. was measured at 298 K; b. wasmeasured at 77 K.

FIG. 7 is a graph of UV-vis spectra of Ir(III) corroles in toluenesolution at 298 K.

FIG. 8 is a graph illustrating the shift in the lower energy Soretcomponent as a function of solvent polarizability (the sodium D line at20° C. was used for n).

FIG. 9 is a graph illustrating spectral shifts of the absorption maximaas a function of solvent polarizability for the weaker Soret and both Qabsorption bands in various solvents.

FIG. 10 is a graph of UV-vis absorption spectra of (top to bottom):1-Ir(tma)₂, 1b-Ir(tma)₂, 1-Ir(py)₂ at room temperature in a broad rangeof solvents; the inset is a graph of the Soret band used for thecalculation of the solvatochromic shifts discussed herein.

FIG. 11 is a graph of normalized excitation profiles of (top to bottom):1-Ir(tma)₂, 1b-Ir(tma)₂, 1-Ir(py)₂ monitored at emission wavelengths of790 and 890 nm.

FIG. 12 is a graph of Raman spectra of 1-Ir(tma)₂, 1b-Ir(tma)₂,1-Ir(py)₂; sample excitation into the Soret was achieved with the 488 nmline of an argon ion laser.

FIG. 13 is a graph of a ¹H NMR spectrum (red) and a graph of a ¹⁹F NMRspectra (blue inserts) of 1-Ir(py)₂.

FIG. 14 is a graph of electronic spectra of the 6-coordinatebis-pyridine metal (III) corroles (top) and the 5-coordinatePPh₃-coordinated metal(III) corroles (bottom), at 2.5 μM concentrationin CH₂Cl₂.

FIG. 15 is a series of graphs illustrating the changes in the electronicstructure in CH₂Cl₂ that demonstrate (from top): the reversibletransformations between 1-Co(py)₂ and 1-Co(PPh₃) upon addition of PPh₃and pyridine; formation of 1-Rh(PPh₃)₂ from 1-Rh(PPh₃); and formation of1-Ir(PPh₃)₂ from 1-Ir(PPh₃).

FIG. 16 is an illustration of the molecular structure of thebis-pyridine Ir(III) corrole 1-Ir(py)₂ (hydrogen atoms omitted).

FIG. 17 is a series of graphs of CV traces of CH₂Cl₂ solutions of the1-M(PPh₃) and 1-M(py)₂ complexes.

FIG. 18 is a series of graphs illustrating changes in the electronicspectra indicating oxidation of 1-Co(PPh₃) (top) and 1-Rh(PPh₃) (bottom)by tris(4-bromophenyl)aminiumhexachloroantimonate (t-4 bpa) in CH₂Cl₂.

FIG. 19 is a series of graphs illustrating changes in the electronicspectra indicating oxidation of 1-Co(py)₂ (top) and 1-Rh(py)₂ (bottom)by t-4 bpa in CH₂Cl₂.

FIG. 20 is a series of graphs illustrating changes in the electronicspectra indicating oxidation by t-4 bpa in CH₂Cl₂ of (from top): a)1-Ir(PPh₃)₂, up to its first oxidation product; b) 1-Ir(PPh₃)₂, startingafter its first oxidation product is formed; and c) 1-Ir(py)₂.

FIG. 21 is a graph of spectroelectrochemical results for a CH₂Cl₂solution of 1-Ir(PPh₃) at 1.0 V vs. Ag/AgCl; the inset is a graph of thespectra of the starting material (red), the first oxidation product(green), and the second oxidation product (blue).

FIG. 22 is a graph of spectroelectrochemical results for a CH₂Cl₂solution of 1-Ir(PPh₃) containing 5 equivalents of PPh₃ at 1.0 V vs.Ag/AgCl; where the starting material is red and the final product ispurple.

FIG. 23 is a graph of electron paramagnetic resonance (EPR) spectrataken at 20 K in frozen toluene solutions (with small amounts of CH₂Cl₂to solvate t-4 bpa for the top two spectra), of the chemically oxidizedforms of (clockwise from top left): a) 1-Co(py)₂; b) 1-Rh(py)₂; and c)1-(py)₂; where the blue traces are the experimental spectra and theblack traces are simulations performed using the SPINCOUNT package.

FIG. 24 is a graph of a 300 MHz ¹H NMR spectrum of 1-Ir(py)₂.

FIG. 25 is a graph of a 300 MHz ¹⁹F NMR spectrum of 1-Ir(py)₂.

FIG. 26 is a graph of an electrospray ionization mass spectrometry(ESI-MS) trace for 1-Ir(py)₂.

FIG. 27 is a graph of a 300 MHz ¹H NMR spectrum of 1-Ir(PPh₃).

FIG. 28 is a graph of a 300 MHz ¹⁹F NMR spectrum of 1-Ir(PPh₃).

FIG. 29 is a graph of an ESI-MS trace for 1-Ir(PPh₃).

FIG. 30 is a graph illustrating changes to the electronic absorptionspectrum of 1-Co(PPh₃) in CH₂Cl₂ upon addition of excess PPh₃.

FIG. 31 is a graph illustrating changes to the electronic absorptionspectrum of 1-Co(PPh₃) in CH₂Cl₂ upon reaction with iodine.

FIG. 32 is a graph illustrating changes to the electronic absorptionspectrum of 1-Rh(PPh₃) in CH₂Cl₂ upon reaction with iodine.

FIG. 33 is a graph illustrating changes to the electronic absorptionspectrum of 1-Ir(PPh₃) in CH₂Cl₂ upon reaction with iodine.

FIG. 34 is a graph of the electronic absorption spectrum of 1-Co(py)₂ in5% pyridine/CH₂Cl₂.

FIG. 35 is a graph of the electronic absorption spectrum of 1-Ir(PPh₃)in 5% pyridine/CH₂Cl₂, illustrating that 1-Ir(PPh₃) is not converted to1-Ir(py)₂ under these conditions.

FIG. 36 is a graph of an EPR spectrum of singly oxidized 1-Co(PPh₃),taken at 20 K in frozen toluene.

FIG. 37 is a graph of an EPR spectrum of singly oxidized 1-Rh(PPh₃),taken at 20 K in frozen toluene.

FIG. 38 is an illustration of the atom numbering scheme used inelectronic structure calculations for compounds according to embodimentsof the present invention; hydrogen atoms are in white, carbon atoms arein grey, nitrogen atoms are in blue, fluorine atoms are in green, andthe metal is in lighter blue; note that the numbering of the corrolering is different from the numbering convention of molecularnomenclature.

FIG. 39 is an illustration of the molecular orbital (MO) surfaces(isovalue=−0.05) calculated for (tpfc)M(NH₃)₂, where M=Rh (left; Coshows similar results) and Ir (right); the topmost MO is the HOMO, whichis followed by HOMO-1, and so on, until the MO above 1a₁ is reached; 1a,is HOMO-13 when M=Rh, HOMO-14 when M=Co, and HOMO-4 when M=Ir.

FIG. 40 is an illustration of the relative energies and spin densitysurfaces (isovalue=−0.002) calculated for [(tpfc)M(NH₃)₂]+ (M=Co, Rh,Ir).

FIG. 41 is an illustration of the relative energies and spin densitysurfaces (isovalue=−0.002) calculated for [(tfc)M(NH₃)₂]+(M=Co, Rh, Ir).

FIG. 42 is an illustration of orbital drawings and energies for[(tfc)Co(NH3)2]+ and [(tpfc)Co(NH3)2]+.

FIG. 43 is an illustration of orbital drawings and energies for[(tfc)Rh(NH3)2]+ and [(tpfc)Rh(NH3)2]+.

FIG. 44 is an illustration of orbital drawings and energies for[(tfc)Ir(NH3)2]+ and [(tpfc)Ir(NH3)2]+.

FIG. 45 is a graph of a ¹H NMR spectrum of a platinum containingmetallocorrole according to embodiments of the present invention.

FIG. 46 is a graph of a correlation spectroscopy (COSY) ¹H NMR spectrumof a platinum containing metallocorrole according to embodiments of thepresent invention.

DETAILED DESCRIPTION

In the following detailed description, compounds are abbreviated in anumber of ways. For example, 5,10,15-tris(pentafluorophenyl)corrolatoiridium(III) (trimethylamine)₂ may be abbreviated as 1,1-Ir(tma)₂, or1-tma. Also,2,3,7,8,12,13,17,18-octabromo-5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis-trimethylamine may be abbreviated as 2, 1b-Ir(tma)₂, or 2-tma.5,10,15-Tris-pentafluorophenylcorrolato-iridium(III) bis-pyridine may beabbreviated as 1-Ir(py)₂, or 1-py.5,10,15-Tris-pentafluorophenylcorrolato-iridium(III) triphenylphosphinemay be abbreviated as 1-Ir(PPh₃), or 1-PPh₃.5,10,15-Tris-pentafluorophenylcorrolato-iridium(III) bis-cyanopyridinemay be abbreviated as 1-Ir(CNpy)₂ or 1-CNpy.5,10,15-Tris-pentafluorophenylcorrolato-iridium(III)bis-4-methoxypyridine may be abbreviated as 1-Ir(Opy)₂ or 1-MeOpy.5,10,15-Tris-pentafluorophenylcorrolato-iridium(III)bis[3,5-bis(trifluoromethyl)pyridine] may be abbreviated as1-Ir((CF₃)_(2py))₂ or 1-(CF₃)₂py.5,10,15-Tris-pentafluorophenylcorrolato-iridium(III)bis(3,5-dichloropyridine-1 may be abbreviated as 1-Ir(Cl_(2py))₂ or1-Cl_(2py). Iridium(I) cyclooctadiene chloride dimer may be abbreviatedas [Ir(cod)Cl]₂. 5,10,15-Tris-pentafluorophenylcorrole may beabbreviated as H₃(tpfc). 5,10,15-Tris-pentafluorophenylcorrolatotrianion may be abbreviated as tpfc.2,3,7,8,12,13,17,18-Octabromo-5,10,15-tris-pentafluorophenylcorrolatotrianion may be abbreviated as Br₈-tpfc. Tris(4-bromophenyl)aminiumhexachloroantimonate may be abbreviated as t-4 bpa. TrimethylamineN-oxide may be abbreviated as tma-N-oxide. Trimethylamine may beabbreviated as tma. Pyridine may be abbreviated as py.

Embodiments of the present invention relate to metallocorrolesrepresented by Formula I.

In Formula I, M is selected from third row transition metals. Each of R₁through R₃ is independently selected aryl groups and heteroaryl groups.Each of X₁ through X₈ is independently H, halides, aldehydes, carboxylicacids, cyanoacetates, sulfonyls, SO₂Cl, SO₃H, SO₂NR₁R₂, CO₂H, COCl,CONR₄R₅, CHO or NO₂, wherein R₄ and R₅ may be the same or different, andeach is selected from H, alkyl, aryl, and heteroaryl; and each of L₁ andL₂ is a binding site or an axial ligand.

According to some embodiments of the present invention, M is an elementselected from late transition metals. Late transition metals may includeOs, Ir, Pt, and Au. In some alternate embodiments, M is an elementselected from W, Os, Ir, Pt, and Au. In another embodiment, M is Ir.

According to an embodiment of the present invention, each of L₁ and L₂is independently a binding site or an axial ligand selected fromtrimethylamine, pyridine, 4-methoxypyridine, 4-cyanopyridine,3,5-dichloropyridine, 3,5-bis-trifluoromethylpyridine.

According to an embodiment of the present invention, each of X₁ throughX₈ is independently selected from H, F, Cl, and Br.

According to an embodiment of the present invention, each of R₁ throughR₃ is independently selected from phenyl, methylphenyl (para-tolyl),4-aminophenyl, dichlorophenyl, 2,6-dichlorophenyl, 2,6-difluorophenyl,pentafluorophenyl, 4-methoxyphenyl, 2,5-dimethoxyphenyl,4-methoxy-2,3,5,6-tetrafluorophenyl,4-(pyrid-2-yl)-2,3,5,6-tetrafluorophenyl,4-(N-methyl-pyrid-2-ylium)-2,3,5,6-tetrafluorophenyl, 4-pyridyl,benzaldehyde, 4-NO₂ benzaldehyde, 3-NO₂ benzaldehyde, 2-NO₂benzaldehyde, 4-Br benzaldehyde, 3-Br benzaldehyde, 2-Cl benzaldehyde,4-CH₃ benzaldehyde, 4-OCH₃ benzaldehyde, 2,5-(OCH₃)₂ benzaldehyde,F₅-benzaldehyde, 4-pyridinecarboxaldehyde, 2-furalaldehyde,mesitaldehyde, 2,6-(OCH₃)₂ benzaldehyde, and 2,6-Cl₂ benzaldehyde. Thealdehyde starting materials will result in a final R group which nolonger bears the aldehyde functionality, but is bound to the corroleframework by the carbon which previously bore the functionality.

According to an embodiment of the present invention, the metallocorroleof Formula I is selected from:2,17-bis(chlorosulfonyl)-5,10,15-tris(pentafluorophenyl)corrolato M;3,17-bis(chlorosulfonyl)-5,10,15-tris(pentafluorophenyl)corrolato M;5,10,15-tris(pentafluorophenyl)-2,17-bis(sulfonic acid)-corrolato M;5,10,15-tris(pentafluorophenyl)-3,17-bis(sulfonic acid)-corrolato M;2,17-bis(piperidinosulfonyl)-5,10,15-tris(pentafluorophenyl)corrolato M;3,17-bis(piperidinosulfonyl)-5,10,15-tris(pentafluorophenyl)corrolato M;5,10,15-triphenylcorrolato M; 5,10,15-tris(4-nitrophenyl)corrolato M;5,10,15-tris(2-nitrophenyl)corrolato M;5,10,15-tris(3-nitrophenyl)corrolato M;5,10,15-tris(4-bromophenyl)corrolato M;5,10,15-tris(3-bromophenyl)corrolato M;5,10,15-tris(2-chlorophenyl)corrolato M;5,10,15-tris(4-methylphenyl)corrolato M;5,10,15-tris(4-methoxyphenyl)corrolato M;5,10,15-tris(2,5-dimethoxyphenyl)corrolato M;5,10,15-tris(4-pyridyecorrolato M;5,10,15-tris(pentafluorophenyl)corrolato M;2,3,7,8,12,13,17,18-octabromo-5,10,15-triphenylcorrolato M; and2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(4-nitrophenyl)corrolato M.

In one embodiment, the metallocorrole of Formula I is5,10,15-tris(pentafluorophenyl)corrolato M.

In another embodiment, the metallocorrole of Formula I is2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(pentafluorophenyl)corrolatoM.

According to an embodiment of the present invention, the metallocorroleof Formula 1 is selected from the group consisting of5,10,15-tris(pentafluorophenyl)corrolato iridium(III) (trimethylamine)₂,2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(pentafluorophenyl) corrolatoiridium(III) (trimethylamine)₂, 5,10,15-tris(pentafluorophenyl)corrolatoiridium(III) (4-methoxypyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III) (pyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III)(4-cyanopyridine)₂, 5,10,15-tris(pentafluorophenyl)corrolatoiridium(III) (3,5-dichloropyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III)(3,5-bis-trifluoromethylpyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III)(triphenylphosphine), and 5,10,15-tris(pentafluorophenyl)corrolato(triphenylphosphine)₂.

Embodiments of the present invention relate to metallocorrolesrepresented by Formula II:

In Formula II, M is a third row transition metal. Each of R₁ through R₆is independently selected from aryl groups and heteroaryl groups. Eachof X₁ through X₁₄ is independently selected from H, halides, aldehydes,carboxylic acids, cyanoacetates, sulfonyls, SO₂Cl, SO₃H, SO₂NR₇R₈, CO₂H,COCl, CONR₇R₈, CHO or NO₂, wherein R₇ and R₈ may be the same ordifferent, and each is selected from H, alkyl, aryl, and heteroaryl.Each of L₁ through L₄ is a bidentate ligand.

In one embodiment, M is an element selected from the group consisting oflate transition metals. In another embodiment, M is Pt.

According to an embodiment, each of X₁ through X₁₄ is independentlyselected from H, F, Cl, and Br.

According to an embodiment, each of R₁ through R₆ is independentlyselected from phenyl, methylphenyl (para-tolyl), 4-aminophenyl,dichlorophenyl, 2,6-dichlorophenyl, 2,6-difluorophenyl,pentafluorophenyl, 4-methoxyphenyl, 2,5-dimethoxyphenyl,4-methoxy-2,3,5,6-tetrafluorophenyl,4-(pyrid-2-yl)-2,3,5,6-tetrafluorophenyl,4-(N-methyl-pyrid-2-ylium)-2,3,5,6-tetrafluorophenyl, 4-pyridyl,benzaldehyde, 4-NO₂ benzaldehyde, 3-NO₂ benzaldehyde, 2-NO₂benzaldehyde, 4-Br benzaldehyde, 3-Br benzaldehyde, 2-Cl benzaldehyde,4-CH₃ benzaldehyde, 4-OCH₃ benzaldehyde, 2,5-(OCH₃)₂ benzaldehyde,F₅-benzaldehyde, 4-pyridinecarboxaldehyde, 2-furalaldehyde,mesitaldehyde, 2,6-(OCH₃)₂ benzaldehyde, and 2,6-Cl₂ benzaldehyde. Thealdehyde starting materials will result in a final R group which nolonger bears the aldehyde functionality, but is bound to the corroleframework by the carbon which previously bore the functionality.

Embodiments of the present invention relate to a method of preparing ametallocorrole by mixing a metallocorrole complex of a third rowtransition metal and trimethylamine N-oxide.

In one embodiment, a metallocorrole complex of a third row transitionmetal is prepared by exposing the mixture of the metallocorrole complexincluding a third row transition metal and any substituted ornon-substituted pyridine ligand to oxygen.

In another embodiment, a brominated metallocorrole complex of a thirdrow transition metal is prepared by reacting a brominated metallocorrolecomprising reacting a metallocorrole complex including a third rowtransition metal with excess Br₂.

Scheme 1 is an illustration of the synthesis of exemplary corrolecomplexes (i.e., Ir(III) corrole complexes) according to an embodimentof the present invention.

Scheme 2 is an illustration of three exemplary metallocorroles accordingto embodiments of the present invention.

Scheme 3 is an illustration of, clockwise from the upper left corner: anIr(III) 2-phenylpyridine prior art complex; an Ir(III) porphyrin priorart complex; non-limiting, exemplary Ir(III) octahedral corrolecomplexes according to the present invention; a non-limiting, exemplaryIr(III) octahedral brominated corrole complex according to the presentinvention; and a non-limiting, exemplary Ir(III) five-coordinate corrolecomplex according to the present invention.

Scheme 4 is an illustration of prior art iridium(III) 2-phenylpyridineand porphyrin complexes along with exemplary metallocorroles accordingto embodiments of the present invention.

Scheme 5 is an illustration of axially ligated prior art rhodium(III),and cobalt(III) corroles and exemplary iridium(III) metallocorrolesaccording to embodiments of the present invention (wherein py representspyridine and PO₃ represents triphenylphosphine).

Corroles are structurally distinct from porphyrins. For example, thegeneric structures of both corrole and porphyrin are shown in Scheme 6below.

As can be seen above, compared to the generic porphyrin structure, thegeneric corrole structure has one less methine bridge in the outer ringstructure, and one more NH proton within the interior of the ring. Thebasic corrole structure is also a member of a lower symmetry group thanthe basic porphyrin structure. In addition, the generic corrolestructure is chiral. Further differences between porphyrin and corroleemerge when these compounds are used as ligands. For example, when usedas a ligand in a metalloporphyrin, porphyrin binds as the dianion. Incontrast, in metallocorroles the corrole ligand binds as a trianionicligand. Additional differences between metallocorroles andmetalloporphyrins are set forth below.

Interest in transition metal corrole complexes has increased recentlydue, in large part, to the development of facile methods for thesynthesis of the stable 5,10,15-tris-pentafluorophenylcorrole (“H₃tpfc”)synthon and of other tris-aryl-substituted corroles. The first facilecorrole syntheses led to scalable preparative procedures that in turnopened the way for the synthesis and study of many first- and second-rowtransition metal corroles. Concurrent with this increased interest, mucheffort has been directed toward the goal of developing newmetallocorrole systems for applications including, but not limited to,medical diagnostics and therapeutics as well as catalysis. Althoughthere has been great interest in metallocorroles, third-row transitionmetal corroles are very rare.

In contrast to first and second row transition metals, third rowtransition metals are significantly more electropositive. Thus, highlyoxidized third row transition metal corrole complexes can be expected toassist in catalytic reactions in which first and second row transitionmetal corrole complexes do not participate. In addition, due to thelarge size of third row transition metal nuclei, these metals have veryhigh spin-orbit couplings. These high spin-orbit couplings lead toeasier singlet-triplet inter-system crossing in the excited state, whichin turn allows for the long-wavelength phosphorescence that is desirablefor many applications. For example, Iridium(III) corrole phosphorescenceis observed at ambient temperature at wavelengths much longer (>800 nm)than those of most other luminescent Ir(III) complexes.

Despite the differences between metallocorroles and metalloporphyrinsdescribed herein, metallocorrole complexes may be used in the same orsimilar applications as their metalloporphyrin analogues. Accordingly,metallocorrole compounds may be used as improved therapeutic agents,catalysts, components of oxygen detectors, and components of organiclight emitting diodes (OLEDs). In particular, metal complexes of triarylcorroles may be used as improved photosensitizers in photodynamictherapy (PDT), as improved anti-cancer agents (e.g., tumor detectionand/or tumor elimination), improved catalysts for inorganic and organicreactions (e.g., aziridination and/or epoxidation reactions), improvedin vivo imaging agents, and improved components of the emissive layer inOLEDs. Further, third row transition metal corrole complexes may be usedas catalysts in water splitting reactions.

Concurrent with the intensified research into metallocorrole complexes,interest in the chemistry of iridium (“Ir”), a third row transitionmetal, also accelerated greatly, owing in part to reports of high-valentoxo and nitrido species as well as other complexes possessing wideranging catalytic activities. While cyclometalated iridium(III)complexes such as [Ir(ppy)₃] (ppy=2-phenylpyridine) phosphoresce insolution with quantum yields of 0.1-0.6 and microsecond lifetimes (near100% internal efficiencies in OLEDs), these characteristics may nottranslate into useful Ir(III) porphyrins. Typically, Ir(III) porphyrinsare stable only when additionally coordinated by CO, hydride, or alkylligands [as in (por)Ir(CO)Cl and (por)Ir—R; where por is porphyrindianion; and R=alkyl or hydride]. Thus, although Ir(III) porphyrins havebeen identified as potentially useful compounds, practical examples havebeen elusive.

In contrast to their porphyrin analogues, the strong σ-donor environmentof corroles stabilizes metals in high oxidation states; this property istypified by stable nitrido chromium(VI) and manganese(VI) species.Although corroles (both metal-free and in complexes withnon-redox-active elements) are prone to oxidation, it is wellestablished that they stabilize transition metals in unusually highoxidation states. Many of these complexes, especially of first-rowtransition metals, exhibit striking reactivity: activation of O₂ bytrivalent chromium, manganese, and iron; catalytic reduction of CO₂ byiron(I) and cobalt(I); iron(IV)-mediated aziridination of olefins;iron(IV) derivatives remain the only non-copper catalysts for theaziridination of olefins by chloramine-T; manganese(III) forms(oxo)manganese(V) during oxygenation catalysis; chromium(III) mediatesthe aerobic oxidation of thiophenol to diphenyl disulfide; and iron(I)and cobalt(I) corroles catalyze the reduction of carbon dioxide. Thesereactivity patterns highlight the role of unusually strong corroleσ-donation in the activation of low-valent metal centers. This sameelectronic property, which accounts for the unusual stability of nitridochromium(VI) and manganese(VI) complexes, is an important factor inbiologically relevant metallocorrole-catalyzed processes. Complexes oftriarylcorroles with group 13-15 elements have been characterized, oftenwith a focus on photophysical properties; for example, a gallium(III)corrole has been shown to be both an in vivo imaging agent and ananticancer drug candidate. Several second-row transition metals alsoform stable corrole complexes: (oxo)molybdenum(V); ruthenium(III), astriply bonded Ru—Ru dimers and nitric oxide bound monomers;rhodium(III), which catalyzes carbene-transfer reactions; andsilver(III).

Because trianionic corroles have the ability to stabilize metals in highoxidation states, they are able to stabilize Ir(III) compounds. As aresult, Ir(III) corroles can be stabilized even by weakly donating axialligands. In addition, corroles bind Ir(III) without the aid ofadditional organic ligands. This is in direct contrast to Ir(III)porphyrins, which are only stable when the metal is further coordinatedby organometallic ligands [such as in (por)Ir(CO)Cl and (por)Ir—R].

The inventive third row transition metal corrole complexes of thepresent invention display several unique features not shared with 3d and4d metallocorrole analogues. In particular, the photophysical propertiesof Ir(III) corroles differ significantly from those of other luminescentmetallocorroles and even other cyclometalated Ir(III) compounds. Ir(III)corrole phosphorescence is observed at ambient temperature [Ge(IV) andSn(IV) corroles emit only at low temperatures] at wavelengths muchlonger (>800 nm) than those of other luminescent Ir(III) complexes. Forexample, 5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis-trimethylamine (“1-Ir(tma)₂”) emits at 792 nm with a 0.35 mslifetime and2,3,7,8,12,13,17,18-octabromo-5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis-trimethylamine (“2-Ir(tma)₂”) emits at 796 nm with a 0.78 mslifetime. The phosphorescence quantum yields vary among Ir(III)corroles, with substantial dependence on corrole ring β-substituents andaxial ligands. Absorption spectra display a strong positivesolvatochromic effect, indicating that the excited state is much morepolar than the ground state. In addition, the compounds disclosed hereindisplay very high thermal- and photo-stability. That is, they remainintact after hours of illumination and heating.

Further differences between the metallocorroles disclosed herein andmetallocorrole complexes of period 4 and 5 elements are highlighted bycomparison of the very rare isostructural 3d Co(III), 4d Rh(III) and 5dIr(III) series. Both the substitutional lability and sites of oxidationreactions change significantly within this Group 9 metallocorroleseries. For example, cobalt(III) corroles are substitutionally labilecompared to either Rh(III) or Ir(III) derivatives. In particular,1-Co(PPh₃) reacts with pyridine to form 1-Co(py)₂ by way of addition andsubstitution reactions, 1-Rh(PPh₃) reacts with pyridine to form1-Rh(PPh₃)(py) by way of an addition reaction, and 1-PPh₃ reacts withpyridine to form 1-Ir(PPh₃)(py) by way of an addition reaction.

In addition, the affinity of five-coordinate derivatives for a sixthligand increases dramatically down the series. For example, addition of100,000 fold excess of triphenylphosphine to 1-Co(PPh₃) produced onlyminor spectral changes, indicating that triphenylphosphine was not addedas a sixth ligand. Adding 6300 and 350 equivalents of triphenylphosphineto 1-Rh(PPh₃) and 1-Ir(PPh₃), respectively, resulted in major spectralchanges, indicating addition of triphenylphosphine as a sixth ligand.Typically, corrolato-chelated metal(III) ions have surprisingly lowaffinity for a sixth ligand. The current results demonstrate that thiseffect becomes much less pronounced moving down the periodic table.Attributed to the stronger Lewis acidity of 4d and especially 5d metalions, such that coordination of a sixth σ-donating ligand becomes muchmore favorable moving down the group.

Surprisingly, the redox potentials show very little variation among thethree corroles, while electron paramagnetic resonance results suggest ashift from corrole- to metal-centered oxidation in moving from 3d and 4dto 5d complexes. For example, the electrochemical data indicated thatthe metal, rather than the macrocycle, is oxidized only in the case ofIr(III/IV), which contrasts with the most recent findings for analogouscobalt (III) corroles.

Similarly, differences can be seen between the metallocorroles disclosedherein and their metalloporphyrin analogues. For example, the planarmacrocyclic framework in both 1-tma and 2-Ir(tma)₂ is quite unlike thatin the case of porphyrins, which tend to saddle or ruffle whenbrominated. Similarly, the main structural features of 1-Ir(py)₂ are: avery planar macrocyclic framework with a root-mean-square atomicdeviation of 0.04 Å out of the plane defined by the N4 coordinationcore; an in-plane metal ion; and two essentially parallel pyridinerings.

The Ir(III) corroles disclosed herein exhibit long-lived phosphorescenceat room temperature, which is very rare for metallocorroles. Moreover,the emission is in the near-infrared (near-IR) range and is readilytuned by the axial ligands and β-pyrrole substituents. Ir(III) corrolesphosphoresce in the near infrared at ambient temperatures with lifetimesthat are shorter than those of other Ir(III) phosphors. These newcompounds may be used for PDT and other medicinal purposes and fordevelopment as whole animal imaging agents as well as components ofoxygen sensors and OLEDs.

According to embodiments of the present invention, a metallocorrole ofFormula I may be synthesized by reacting H₃tpfc with excess [M(cod)Cl₂](wherein M is a third row transition metal and cod is cyclooctadiene)and K₂CO₃ in hot tetrahydrofuran (THF) under argon (“Ar”) to form(tpfc)M(cod), which may be converted to an axially tma-ligated Ir(III)complex upon addition of tma N-oxide and exposure to the atmosphere.

In one exemplary embodiment, the synthesis of5,10,15-tris-pentafluorophenylcorrole (“H₃tpfc”) may be accomplished bya modified version of the standard procedure outlined in “Solvent-FreeCondensation of Pyrrole and Pentafluorobenzaldehyde: A Novel SyntheticPathway to Corrole and Oligopyrromethenes” Organic Letters. 1999, 1,599-602, the entire content of which is incorporated herein byreference. For example, H₃tpfc may be synthesized by adding a solutionof trifluoroacetic acid in CH₂Cl₂ to warm pentafluorobenzaldehyde, withrapid stirring. Freshly distilled pyrrole may be added to form a viscousred solution. CH₂Cl₂ may also be added with brief stirring. DDQ may beadded slowly to oxidize the macrocycle. The product may be purified bysuccessive chromatographic treatments with CH₂Cl₂:hexanes on silica, andrecrystallization from hot pentane.

According to embodiments of the present invention, a metallocorrole ofFormula II may be synthesized by suspending an excess of M(cod)Cl₂(wherein M is a third row transition metal and cod is cyclooctadiene)and K₂CO₃ in THF under argon. The suspension may be reacted with H₃tpfcheating at reflux until no more red fluorescence is detected. Thesolution may be evaporated, and the residue may be taken up in CH₂Cl₂.Column chromatographic separation in hexanes/CH₂Cl₂ may provide solutionfrom which the metallocorrole may be recovered by. An example of such asynthesis is illustrated in Scheme 7 below.

According to one embodiment, a metallocorrole complex including tungsten(“W”) could be synthesized. In such a synthesis, an excess ofW(1,5-cod)(CO)₄ and K₂CO₃ could be suspended in THF under argon, andH₃tpfc could be added. The reaction mixture could be heated at refluxuntil no more red fluorescence could be detected. The mixture could thenbe opened to air, and pyridine could be added. After 1 hour, the mixturecould be evaporated, and the residue could be taken up in CH₂Cl₂. Columnchromatographic separation in hexanes/CH₂Cl₂ could provide a solutionfrom which (tpfc)W(py)₂ could be recovered by evaporation. Based on thebehavior of tungsten and osmium in porphyrin complexes, we propose thatthese metallocorroles might form oxo complexes when exposed to oxygenunder certain conditions.

According to another embodiment, a metallocorrole complex includingosmium (“Os”) could be synthesized. In such a synthesis, an excess ofOsCl₃ and K₂CO₃ could be suspended in THF under argon, and H₃tpfc couldbe added. The reaction mixture could be heated at reflux until no morered fluorescence could be detected. The mixture could then be opened toair, and pyridine could be added. The mixture could then be evaporated,and the residue could be taken up in CH₂Cl₂. Column chromatographicseparation in hexanes/CH₂Cl₂ could provide a solution from which(tpfc)Os(py)₂ could be recovered by evaporation.

The following examples are presented for illustrative purposes only anddo not limit the scope of the present invention.

Silica gel for column chromatography (Silica Gel 60, 63-200 micron mesh)was purchased from EMD Chemicals. Solvents, such as THF, toluene,CH₂Cl₂, hexanes, and methanol, were purchased from EMD Chemicals or theVWR stockroom at the California Institute of Technology. Most startingmaterials for syntheses were purchased from Sigma-Aldrich and usedwithout further purification. Exceptions include pyrrole andpentafluorobenzaldehyde, which were both purified by vacuum distillationbefore use. Tetrabutylammonium hexafluorophosphate, which was used as asupporting electrolyte in the CV experiments, was also purchased fromSigma-Aldrich and used without further purification. Electrodes for CVwere purchased from CH Instruments.

The synthesis of 5,10,15-tris-pentafluorophenylcorrole (“H₃tpfc”) wasaccomplished by a modified version of the standard procedure outlined in“Solvent-Free Condensation of Pyrrole and Pentafluorobenzaldehyde: ANovel Synthetic Pathway to Corrole and Oligopyrromethenes” OrganicLetters. 1999, 1, 599-602, the entire content of which is incorporatedherein by reference. The cobalt(III) and rhodium(III) corroles wereavailable from previous studies. Compounds 1-Ir(tma)₂ and 1b-Ir(tma)₂have only been reported in a previous communication, hence theirsyntheses are summarized below along with those of the new corroles.According to one embodiment, H₃tpfc was synthesized by the followingroute. 140 μL of a solution of 0.5 mL of trifluoroacetic acid in 5 mL ofCH₂Cl₂ was added to 1.73 mL of warm (liquid) pentafluorobenzaldehyde,with rapid stirring. Addition of 1.46 mL of freshly distilled pyrroleresulted in the rapid formation of a viscous red solution. After 10minutes, 20 mL of CH₂Cl₂ was added and the mixture was allowed to stirbriefly, followed by slow addition of 3.84 g of DDQ to oxidize the newlyformed macrocycle. Purification was accomplished by successivechromatographic treatments with 6.5:3.5 CH₂Cl₂:hexanes and 8.5:1.5CH₂Cl₂:hexanes on silica, followed by recrystallization from hotpentane.

Example 1

5,10,15-tris-pentafluorophenylcorrolato-iridium(III) bis-trimethylamine,(“1-Ir(tma)₂”). 1-Ir(tma)₂ was obtained in 27% yield via reaction ofH₃tpfc with excess [Ir(cod)Cl₂] (cod=cyclooctadiene) and K₂CO₃ in hottetrahydrofuran (THF) under argon (“Ar”) to form (tpfc)Ir(I)(cod), whichwas converted to an axially tma-ligated Ir(III) complex upon addition oftma N-oxide and exposure to the atmosphere. H₃tpfc (80 mg), [Ir(cod)Cl]₂(335 mg), and K₂CO₃ (140 mg) were dissolved/suspended in 150 mL ofdegassed THF, and the mixture was heated at reflux under argon for 90min (until corrole fluorescence was negligible to the eye upon long-waveirradiation with a hand-held lamp). Tma N-oxide (110 mg) was added, andthe solution was allowed to slowly cool to room temperature while opento the laboratory atmosphere. Column chromatography of the black mixture(silica, 4:1 hexanes:CH₂Cl₂) provided an auburn solution, from whichpurple crystals of (tpfc)Ir(III)(tma)₂ (30 mg, 27% yield) could be grownby slow evaporation. ¹H NMR (CDCl₃): δ 8.90 (d, 2H, J=4.2), 8.50 (d, 2H,J=5.1), 8.38 (d, 2H, J=4.5), 8.09 (d, 2H, J=4.2), −2.95 (s, 18H). ¹⁹FNMR (CDCl₃): δ −138.38 (m, 6F), −154.89 (m, 3F), −163.27 (m, 6F). MS(ESI): 1105.1 ([M⁺]), 1046.0 ([M⁺-tma]), 986.5 ([M⁺-2tma]). UV-vis(CH₂Cl, nm, ∈×10⁻³M⁻¹ cm⁻¹): 388 (47), 412 (56), 572 (14), 640 (5.3).

Example 2

2,3,7,8,12,13,17,18-octabromo-5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis-trimethylamine, (“1b-Ir(tma)₂”). Compound I-Ir(tma)₂ (15 mg) and Br₂(70 μL) were dissolved in 20 mL MeOH and stirred overnight. Columnchromatography (silica, 4:1 hexanes:CH₂Cl₂) of the red mixture provideda ruddy solution from which purple crystals of 1b-Ir(tma)₂ (15 mg, 63%yield) could be grown by addition of methanol followed by slowevaporation. ¹H NMR (CDCl₃): δ −2.60 (s, 18H). ¹⁹F NMR (CDCl₃): δ−137.78 (d/d, 2F, ³J=35.1, ⁴J=18.3), −138.54 (d/d, 4F, ³J=33.9,⁴J=17.1), −152.89 (m, 3F), −163.38 (m, 4F), −163.70 (m, 2F). MS (ESI):1616.4 ([M⁺-2tma]). UV-vis (CH₂Cl₂, nm, ∈×10⁻³ M⁻¹ cm⁻¹): 404 (61), 424(70), 580 (16), 654 (7.3).

As would be understood, although bromination is described, otherhalogenated corrole macrocycles can be accessed via literature methods.

Example 3

5,10,15-tris-pentafluorophenylcorrolato-iridium(III) bis-pyridine,(“1-Ir(py)₂”). H₃tpfc (40 mg), [Ir(cod)Cl]₂ (170 mg), and K₂CO₃ (70 mg)were dissolved/suspended in 75 mL of degassed THF, and the mixture washeated at reflux under argon for 90 min. Pyridine (1 mL) was added, andthe solution was allowed to slowly cool to room temperature while opento the laboratory atmosphere. Column chromatography of the forest greenmixture (silica, 4:1 hexanes:CH₂Cl₂ followed by 3:2 hexanes:CH₂Cl₂)provided a bright green solution, from which thin, green crystals of1-Ir(py)₂ (26 mg, 50% yield) could be grown by addition of methanolfollowed by slow evaporation. ¹H NMR (CDCl₃): δ 8.84 (d, 2H, J=4.5),8.53 (d, 2H, J=4.8), 8.32 (d, 2H, J=4.8), 8.17 (d, 2H, J=4.5), 6.21 (t,2H, J=7.8), 5.19 (t, 4H, J=7.0), 1.72 (d, 4H, J=5.1). ¹⁹F NMR (CDCl₃): δ−138.68 (m, 6F), −154.84 (t, 2F, J=22.2), −155.20 (t, 1F, J=22.2),−163.28 (m, 4F), −163.65 (m, 2F). MS (ESI): 1144.1 ([M⁺]). UV-vis(CH₂Cl₂, nm, ∈×10⁻³M⁻¹ cm⁻¹): 390 (28), 412 (43), 582 (12), 619 (6.5).

Example 4

5,10,15-tris-pentafluorophenylcorrolato-iridium(III) triphenylphosphine,(“1-Ir(PPh₃)”). H₃tpfc (40 mg), [Ir(cod)Cl]₂ (170 mg), and K₂CO₃ (70 mg)were dissolved/suspended in 75 mL of degassed THF, and the mixture washeated at reflux under argon for 90 min. Triphenylphosphine (260 mgdissolved in 5 mL THF) was added, and the solution was heated at refluxfor another half hour under laboratory atmosphere before being allowedto cool to room temperature. Column chromatography of the deep greenmixture (silica, 3:1 hexanes:CH₂Cl₂) provided a bright red-orangesolution, which could be evaporated to give 1-Ir(PPh₃) (30 mg, 64%yield) as a ruby-colored solid. ¹H NMR (CDCl₃): δ 8.67 (d, 2H, J=4.5),8.36 (d, 2H, J=5.1), 8.18 (d, 2H, J=5.1), 8.00 (d, 2H, J=4.5), 6.98 (t,3H, J=7.2), 6.69 (t, 6H, J=6.9), 4.52 (d/d, 6H, ³J=19.5, ⁴J=3.6). ¹⁹FNMR (CDCl₃): δ −137.44 (m, 6F), −154.05 (m, 3F), −162.54 (m, 3F). MS(ESI): 1248.1 ([M⁺]). UV-vis (CH₂Cl₂, nm, ∈×10⁻³ M⁻¹ cm⁻¹): 398 (66),554 (8.8), 588 (6.7).

Example 5

5,10,15-tris-pentafluorophenylcorrolato-iridium(III) bis-cyanopyridine,(“1-Ir(CNp_(Y))₂”). H₃tpfc (40 mg), [Ir(cod)Cl]₂ (170 mg), and K₂CO₃ (70mg) were dissolved/suspended in 75 mL of degassed THF, and the mixturewas heated at reflux under argon for 90 min. 4-Cyanopyridine (105 mg)was added, and the solution was allowed to slowly cool to roomtemperature while open to the laboratory atmosphere. Columnchromatography of the red-green mixture (silica, 4:1 hexanes:CH₂Cl₂followed by 2:3 hexanes:CH₂Cl₂) provided a bright red solution, whichupon evaporation provided 1-Ir(CNpy)₂ (36 mg, 66% yield) as a purplesolid. ¹H NMR (CDCl₃): δ 8.91 (d, 2H, J=4.5), 8.60 (d, 2H, J=5.1), 8.39(d, 2H, J=4.8), 8.26 (d, 2H, J=4.5), 5.43 (d/d, 4H, ³J=6.9, ⁴J=−4.2),1.75 (d/d, 4H, ³J=6.9, ⁴J=−3.9). ¹⁹F NMR (CDCl₃): δ −138.38 (d/d, 2F,³J=34.8, ⁴J=17.4), −138.95 (d/d, 4F, ³J=34.8, ⁴J=17.4), −153.75 (t, 2F,J=22.5), −154.11 (t, 1F, J=22.2), −162.48 (m, 4F). −162.84 (m, 2F). MS(ESI): 1089.0 ([M⁺-4-CNpy]), 986.1 ([M⁺-2(4-CNpy)]) UV-vis (CH₂Cl₂, nm,∈×10⁻³ M⁻¹ cm⁻¹): 388 (8.8), 406 (14), 580 (4.2), 608 (2.8).

Example 6

5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis-4-methoxypyridine, (“1-Ir(MeOpy)₂”). H₃tpfc (40 mg), [Ir(cod)Cl]₂(170 mg), and K₂CO₃ (70 mg) were dissolved/suspended in 75 mL ofdegassed THF, and the mixture was heated at reflux under argon for 90min. 4-Methoxypyridine (110 mg) was added, and the solution was allowedto slowly cool to room temperature while open to the laboratoryatmosphere. Column chromatography of the red-green mixture (silica, 4:1hexanes:CH₂Cl₂ followed by 2:3 hexanes:CH₂Cl₂) provided an olivesolution, which upon evaporation provided 1-Ir(MeOpy)₂ (28 mg, 50%yield) as a dark green solid. ¹H NMR (CDCl₃): δ 8.81 (d, 2H, J=4.2),8.49 (d, 2H, J=4.5), 8.31 (d, 2H, J=4.5), 8.12 (d, 2H, J=3.9), 4.69(d/d, 4H, ³J=7.2, ⁴J=−4.5), 2.93 (s, 6H), 1.56 (m, 4H). ¹⁹F NMR (CDCl₃):δ −138.40 (d/d, 2F, ³J=35.7, ⁴J=17.4), −138.64 (d/d, 4F, ³J=35.7,⁴J=17.4), −154.98 (t, 2F, J=22.5), −155.35 (t, 1F, J=22.4), −163.33 (m,4F). −163.69 (m, 2F). UV-vis (CH₂Cl₂, nm, ∈×10⁻³ M⁻¹ cm⁻¹): 394 (42),412 (57), 394 (42), 412 (57).

Example 7

5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis[3,5-bis(trifluoromethyl)pyridine], [“1-Ir((CF₃)₂py)₂”]. H₃tpfc (40mg), [Ir(cod)Cl]₂ (170 mg), and K₂CO₃ (70 mg) were dissolved/suspendedin 75 mL of degassed THF, and the mixture was heated at reflux underargon for 90 min. 3,5-bis-trifluoromethylpyridine (215 mg) was added,and the solution was allowed to slowly cool to room temperature whileopen to the laboratory atmosphere. Column chromatography of the deepgreen mixture (silica, 4:1 hexanes:CH₂Cl₂ followed by 100% CH₂Cl₂)provided a red-green solution, which upon evaporation provided1-Ir((CF₃)_(2py))₂ (13 mg, 20% yield) as a filmy red-purple solid. ¹HNMR (CDCl₃): δ 9.00 (d, 2H, J=4.2), 8.70 (d, 2H, J=4.8), 8.44 (d, 2H,J=4.8), 8.38 (d, 2H, J=4.2), 6.65 (s, 2H), 1.97 (s, 4H). ¹⁹F NMR(CDCl₃): δ=−64.29 (t, 12F, J=7.5), −138.47 (m, 6F), −153.52 (t, 2F,J=22.2), −153.82 (m, 1F), −162.35 (m, 6F). UV-vis (CH₂Cl₂, nm, ∈×10⁻³M⁻¹cm⁻¹): 384 (9.7), 406 (15), 580 (4.5), 602 (2.8).

Example 8

5,10,15-tris-pentafluorophenylcorrolato-iridium(III)bis(3,5-dichloropyridine], [“1-Ir(Cl₂py)₂”]. H₃tpfc (40 mg),[Ir(cod)Cl]₂ (170 mg), and K₂CO₃ (70 mg) were dissolved/suspended in 75mL of degassed THF, and the mixture was heated at reflux under argon for90 min. 3,5-dichloropyridine (150 mg) was added, and the solution wasallowed to slowly cool to room temperature while open to the laboratoryatmosphere. Column chromatography of the bright green mixture (silica,4:1 hexanes:CH₂Cl₂ followed by 100% CH₂Cl₂) provided a vivid greensolution, from which dark green crystals of 1-Ir(Cl₂py)₂ (27 mg, 47%yield) could be grown by addition of toluene followed by slowevaporation. ¹H NMR (CDCl₃): δ 8.91 (d, 2H, J=4.2), 8.64 (d, 2H, J=4.5),8.40 (d, 2H, J=4.5), 8.30 (d, 2H, J=4.2), 6.16 (t, 2H, J=1.8), 1.52 (d,4H, J=1.8). ¹⁹F NMR (CDCl₃): δ −137.49 (d/d, 2F, ³J=34.8, ⁴J=17.7),−137.71 (d/d, 4F, ³J=34.8, ⁴J=17.1), −153.87 (t, 2F, J=22.5), −154.28(t, 1F, J=22.2), −162.39 (m, 4F). −162.82 (m, 2F). UV-vis (CH₂Cl₂, nm,∈×10⁻³ M⁻¹ cm⁻¹): 390 (26), 406 (38), 580 (12), 608 (7.3).

Nuclear Magnetic Resonance Spectroscopy (“NMR”): ¹H and ¹⁹F NMRspectrometric measurements were performed on CDCl₃ solutions of eachcompound at room temperature using a Varian Mercury 300 MHz NMRspectrometer. ¹H chemical shifts are reported relative to solvent peaksand ¹⁹F chemical shifts are reported relative to a saved, external CFCl₃standard.

Mass spectrometry: Mass spectrometric measurements were performed onCH₃OH solutions of each compound by electrospray ionization into aThermofinnigan LCQ ion trap mass spectrometer.

X-ray Crystallography: Concentrated CH₂Cl₂/CH₃OH solutions of corroles1-Ir(tma)₂, 1b-Ir(tma)₂, and 1-Ir(py)₂ were allowed to undergo slowevaporation from scintillation vials. The resultant crystals weremounted on a glass fiber using Paratone oil and then placed on a BrukerKappa Apex II diffractometer under a nitrogen stream at 100K. TheSHELXS-97 program was used to solve the structures.

Cyclic voltammetry: Cyclic voltammetry (“CV”) was carried out with aWaveNow USB Potentiostat/Galvanostat (offered by Pine ResearchInstrumentation) using Pine Aftermath Data Organizer software. A threeelectrode system were used and consisted of platinum wire workingelectrode, a platinum wire counter electrode, and an Ag/AgCl referenceelectrode. The CV measurements were done at ambient temperature andunder argon atmosphere using dichloromethane solutions, 0.1 M intetrabutylammonium perchlorate (TBAP, Fluka, recrystallized twice fromabsolute ethanol) and 10⁻³ M in substrate. The scan rate was 100 mV/secand the E_(1/2) value for oxidation of ferrocene under these conditionswas 0.55 V.

Cyclic voltammetry (“CV”, FIG. 4) reveals that Ir(III) corroles are veryelectron-rich: Ir(II) is not electrochemically accessible and Ir(IV) isobtained at relatively low potentials. These particular CV measurementswere made in degassed CH₂Cl₂ solutions under Ar containing 0.3 MNEt₄BF₄, using a glassy carbon disk working electrode, a Pt wireauxiliary electrode, and a Ag/AgCl quasi-reference electrode. Only 2could be reduced within the electrochemical window of the solvent andthe reversibility of that process (E_(1/2)=−1.21 V vs. SCE) isconsistent with the formation of a corrole radical anion rather thanIr(II), as the latter would rapidly release its axial ligand(s) and mostlikely also dimerize. All other reversible electron transfer processesare also obtained at quite positive potentials. Guided by theelectrochemistry of other metallocorroles, the first and second redoxprocesses of 1 (E_(1/2)=+0.66 and +1.28 V vs. SCE, respectively) maytentatively be assigned as metal-centered (Ir^(III)/Ir^(Iv)) andcorrole-centered (tpfc/tpfc⁺), respectively. As full bromination at theβ-pyrrole positions is known to upshift the potentials ofmetallocorroles by a few hundred mV, the feature at +1.19 V can beassigned to the Ir^(III)/Ir^(IV) couple in 2. Our data show clearly thatIr(III) is more electron-rich in corroles than in other coordinationenvironments. The E_(1/2) value for the [(tpp)Ir]⁺/[(tpp)Ir]²⁺(tpp=tetraphenylporphyrinato) redox couple is about +1.4 V vs. SCE, andIr^(III)/Ir^(IV) processes in cyclometalated bpy complexes also occur atmuch more positive potentials than in 1.

Electron Paramagnetic Resonance (“EPR”): Solutions for EPR were preparedby adding 25 μL of either a 1 mM CH₂Cl₂ solution oftris(4-bromophenyl)aminiumhexachloroantimonate (“t-4 bpa”) or a 1 mMtoluene solution of elemental iodine to 150 μL of a 2 mM toluenesolution of the corrole being examined. EPR spectroscopy was performedusing a Bruker EMX Biospin instrument, with a Gunn diode microwavesource. Solutions were glassed by rapid freezing in liquid nitrogen, andspectra were then taken at 20 K using liquid helium as coolant. TheSPINCOUNT package was used to simulate EPR parameters.

UV-vis Absorption Spectroscopy: Electronic absorption measurements wereperformed on solutions of each compound in CH₂Cl₂, using aHewlett-Packard 8452A Diode Array Spectrophotometer. Extinctioncoefficients were calculated from measurements performed ongravimetrically produced CH₂Cl₂ solutions of each corrole at variableconcentrations. UV-visible spectroelectrochemical experiments wereperformed with an optically transparent platinum thin-layer electrode asworking electrode, a platinum wire counter electrode, and an Ag/AgClreference electrode, at ambient temperature and under argon atmosphereusing dichloromethane solutions, 0.5 M in TBAP and 0.1-0.1 mM insubstrate. Potentials were applied with a WaveNow USBPotentiostat/Galvanostat. Time-resolved UV-visible spectra were recordedwith a Hewlett-packard Model 8453 diode array rapid-scanningspectrophotometer.

Solution state UV-vis absorption spectra were measured using a Cary 50scanning spectrophotometer with a pulsed xenon lamp as the excitationsource. The error in reported wavelength values is at most 0.5 nm.Extinction coefficients were measured for gravimetrically preparedsolutions of iridium corroles in toluene, and should be accurate to±10%.

Steady-state and time-resolved emission measurements were conducted atthe Beckman Institute Laser Resource Center. Emission spectra wererecorded on samples dissolved in solution (room temperature) or frozenglass (77 K). Samples were degassed by three freeze-pump-thaw cycles.For steady-state emission spectra, the 496.5 nm line of an argon ionlaser (Coherent Inova 70) was used to excite samples. Right angleemission was collected via with a Melles Griot Fiber Optic Spectrometer(MGSPEC-2048-SPU). Quantum yields were obtained by comparing signalintensity to a tetraphenylporphyrin standard. Absorption values for thesamples at 496.5 nm were recorded on a Hewlett-Packard 8451A diode arrayspectrophotometer.

For time-resolved measurements, samples were excited at 440 nm. Pulsesof 8 ns duration from the third harmonic of a Q-switched Nd:YAG laser(Spectra-Physics Quanta-Ray PRO-Series) operating at 10 Hz were used topump an optical parametric oscillator (OPO, Spectra-Physics Quanta-RayMOPO-700) to provide laser pulses at 440 nm. Emitted light was detectedwith a photomultiplier tube (PMT, Hamamatsu R928). PMT current wasamplified and recorded using a transient digitizer (Tektronix DSA 602).

Excitation spectra were recorded on a Jobin Yvon Spex Fluorolog-3-11.Sample excitation was achieved via a xenon arc lamp with a monochromatorproviding wavelength selection. The excitation wavelength was scannedbetween 300 nm and 700 nm and recorded at 790 nm and 890 nm. Slits of 2and 10 nm bandpass were used for excitation and emission, respectively.Right angle light emission was sorted using a monochromator and fed intoa Hamamatsu R928P photomultiplier tube with photon counting. Short andlong pass filters were used where appropriate.

Resonance Raman spectra were recorded using the 488 nm line of an argonion laser (Coherent Inova 70). Scattered light was sorted by a 0.75 mspectrograph (Spex 750M) and detected with a liquid-nitrogen-cooled CCD(Princeton Instruments).

The refraction of the sodium D line at 20° C. in a given solvent wastaken to represent its refractive index, n_(D) ²⁰, or simply n. Thepolarizability of a solvent [f(n)] is related to its refractive indexvia the following relationship: f(n)=(n²−1)/(2n²+1) [Lakowicz, Joseph R.Principles of Fluorescence Spectroscopy, 2^(nd) Ed. 1999, pg. 189]. Theextent of the solvatochromic effect exhibited by an absorbing species ina given solvent is then determined by the slope of the lineE_(f)=E_(v)−(solv)[f(n)], where E_(f) is the absorption energy in thesolvent, E_(v) is the absorption energy in vacuum, and (solv) is afactor related to the magnitude of the change in the dipole moment ofthe chromophore upon excitation. In this formalism, the y-intercept ofthe line is equal to the theoretical gas-phase absorption energy of thetransition under examination. We have made our solvatochromism plots bysetting this value equal to zero and plotting the extent of red-shiftingin a variety of solvents. This allows for facile comparison of the threecorroles, such that the steepness of the slope scales with the magnitudeof the separation between the ground and excited state dipole moments.In all cases, the excited state is more polar than the ground state.

A stable six-coordinate (tpfc)Ir(tma)₂ complex (1-Ir(tma)₂, Scheme 1)was obtained as described above. As described above, an octabrominatedcomplex ((Br₈-tpfc)Ir(tma)₂(1b-Ir(tma)₂, Scheme 1) was obtained from1-Ir(tma)₂. Both iridium(III) derivatives were characterized by nuclearmagnetic resonance (NMR) spectroscopy, mass spectrometry (MS), X-raycrystallography, UV-vis spectroscopy, and cyclic voltammetry (CV). Theplanar macrocyclic framework in both 1-Ir(tma)₂ and 1b-Ir(tma)₂ is quiteunlike that in the case of porphyrins, which tend to saddle or rufflewhen brominated. In addition, the electrochemical data indicated thatthe metal, rather than the macrocycle, is oxidized to Ir(IV) in bothcomplexes, which contrasts with most recent findings for analogouscobalt(III) corroles.

Owing to their low-spin d⁶ electronic configuration, iridium(III)corroles display highly resolved NMR spectra characteristic ofdiamagnetic complexes. This is shown in FIG. 13 for 1-Ir(py)₂, where the¹H NMR spectra disclose the four β-pyrrole CH proton resonances asdoublets with J coupling constants of about 4.5 Hz at 8-9 ppm and theaxial ligand resonances at high field due to the diamagnetic ringcurrent effect of the aromatic corrole. The pyridine proton resonancesfor 1-Ir(py)₂ are more shifted than those of the PPh₃ moiety in Ir(PPh₃)(both relative to their position in the absence of a metal center) dueto the much closer proximity of these former protons to the corrolering. The coordination number (6 for the bis-pyridine complex 1-Ir(py)₂and 5 for the triphenylphosphine complex 1-Ir(PPh₃)) can be deduced fromthe ¹H NMR spectra via integration of the relevant proton resonances.The same information is also accessible from the ¹⁹F NMR spectra (FIG.13, inset), since the C_(2v) symmetry of 1-Ir(py)₂ dictates anequivalence between the above- and below-plane ortho- and meta-fluorineatoms on each C₆F₅ ring, resulting in six total ¹⁹F NMR peaks for thecomplex.

The red shifts of the principal features in the electronic spectrum of 2relative to 1 (8-16 nm, FIG. 3) are similar to those observed uponbromination of other metallocorroles, but the intense Soret band systemis uniquely split, as are the Q-bands (roughly 70 nm). Without beinglimited by theory, the shoulders at 448 and 458 nm for 1 and 2,respectively, may be attributable to MLCT transitions, and the couplingsto these excited states may give rise to large splittings of thecorrole-based π-π* states. Based on HOMO and LUMO energies extractedfrom the redox potentials of 2, the MLCT transitions should fall in the400-500 nm region of the visible spectrum.

The molecular structures of 1 and 2 (FIG. 5) reveal that theirmacrbcyclic frameworks are isostructural, with the iridium atom locatedin the plane of an essentially flat corrole. The Ir—N axial bonds areabout 0.2 Å longer than the in-plane Ir—N equatorial bonds, as might beexpected. One notable difference between 1 and 2 is that the aryl ringsare nearly perpendicular with respect to the corrole in the latter,possibly to avoid steric clash with the bromine atoms. The structure of2 is distinctly different from those of analogous tetraarylporphyrins,where β-pyrrole bromination induces large distortions of the macrocyclethat produce dramatic red shifts in UV-vis absorptions and higherreduction potentials. For iridium corroles, the 530 mV upshift in thepotential of 2 vs. 1 may imply major Br-induced electronic effects.

Emission spectra were recorded in toluene at 298 and 77 K (FIG. 6). Thespectra display two intense features separated by approximately 1400cm⁻¹. It is likely that a ring-based vibration is excited in thetransition to the lower energy component.

According to embodiments of the present invention, a corrole can readilyaccommodate a 5d transition metal. The electron transfer processesdemonstrated for 1 and 2 suggest that they may prove useful as redoxcatalysts.

At low temperature, the higher energy emission maximum of each Ir(III)corrole blue shifts by 10 nm (a rigidochromic effect indicating that thetransition involves charge transfer) (FIG. 6 b). The narrow linewidthand ˜1400 cm⁻¹ spacing suggest that the emission is from π→π* excitedstate. Electronic structure calculations place an occupied orbital withmetal character close to the HOMO in related Ir(III) corroles,indicating that ³MLCT states will be near those of the lowestcorrole-localized excited states. The ³MLCT state may also be theemissive state in other cyclometalated Ir(III) complexes.

Luminescence quantum yields and lifetimes in degassed and aeratedtoluene solutions at room temperature (and lifetimes at 77 K) are setout in Table 1. 1-Ir(tma)₂ and 1b-Ir(tma)₂ have relatively shortlifetimes and low quantum yields. 1-Ir(py)₂ exhibits a much higherluminescence quantum yield (1.2%) and a longer lifetime. These resultsindicate that Ir(III)-corrole photophysical properties may depend on thenature of the axial ligand.

TABLE 1 Photophysical data for Ir(III) corroles in toluene solutions,measured at 298 K unless noted otherwise. Compound 1-Ir(tma)₂1b-Ir(tma)₂ 1-Ir(py)₂ Φ_(ph) ^(b)  3.3 × 10⁻⁴  3.9 × 10⁻³  1.2 × 10⁻²λ_(Ar) (nm)/τ_(Ar)(μs) 788/0.220 795/1.19 792/4.91 τ_(air) ^(c) (μs)0.170 0.760 0.380 λ_(77K) (nm)/τ_(Ar) (μs) 786/2.77  786/4.72 793/7.69k_(r) (s⁻¹) 1.5 × 10³ 3.28 × 10³  2.44 × 10³  k_(nr) (s⁻¹) 4.54 × 10⁶ 8.4 × 10⁵ 2.0 × 10⁵ ^(b)Luminescence quantum yields were standardizedagainst free-base tetraphenylporphyrin (Φ_(f) = 0.13 in toluene solutionat 298 K). ^(c)Measured under atmospheric conditions.

UV-vis absorption spectra (FIG. 7) of the three Ir(III) corroles exhibitsplit Soret (S₀→S₂) and Q (S₀→S₁) bands. The splitting of the Soretbands is 1400-1700 cm⁻¹ in all cases; the Q bands are split by roughly1800 cm⁻¹ in the spectra of 1-Ir(tma)₂ and 1b-Ir(tma)₂ but only by 1000cm⁻¹ in the spectrum of 1-Ir(py)₂.

The effect of solvent polarizability on Ir(III)-corrole spectra wasinvestigated to probe the extent of charge transfer in initially formedelectronic excited states. UV-vis spectra were obtained in a variety ofsolvents: Soret band maxima were plotted against polarizability f (FIG.8), defined as f(n)=(n²−1)/(2n²+1), where n is the refractive index ofthe solvent. (The ground states are relatively nonpolar, so inclusion ofa solvent dielectric term is not appropriate.) The strong negativecorrelation (R²>0.9) between the polarizability of the solvent and theenergy of the Soret transition indicates that in each case the excitedstate is substantially more polar than the ground state. The Q bandmaxima display a similar trend. The striking solvatochromic behavior ofIr(III) corroles may be exploited in optical sensors as well as otherapplications requiring solvent-based tuning of absorption and emissionproperties.

Although the Soret solvatochromic shifts of 1-Ir(tma)₂ and 1-Ir(py)₂ aresimilar, 1b-Ir(tma)₂ exhibits a somewhat weaker trend. Without beinglimited by theory, this trend may be attributable to bromine atom“prepolarization” of the electron density on the corrole, therebydecreasing the change in dipole moment upon excitation. Alternatively,the observed trend may result from differences in the polarity of theexcited state initially formed by each of the compounds.

According to embodiments of the present invention, Ir(III) corrolesphosphoresce in the near infrared region at ambient temperatures withlifetimes and quantum yields that may depend on the nature of the axialligands. According to the emission band shapes and vibronic splittingstaken together with results from electronic structure calculations, thephosphorescence of the compounds according to the present invention maybe attributable to a transition from a corrole π→π* triplet state thatlikely has some ³MLCT character.

TABLE 2 Slopes and fitting values for solvatochromic effects on eachabsorption band in the iridium(III) corroles; the correlation values forthe Q bands of 1b-Ir(tma)₂ are probably poor due to the low intensitiesof those bands at the concentrations examined. Comound Band Slope ofShift (f/cm⁻¹) Correlation R² 1-Ir(tma)₂ First Soret −3200 0.90 SecondSoret −4600 0.90 First Q band −2100 0.77 Second Q band −1800 0.911b-Ir(tma)₂ First Soret −2500 0.78 Second Soret −2900 0.95 First Q band−1000 0.60 Second Q band −850 0.25 1-Ir(py)₂ First Soret −4300 0.90Second Soret −5000 0.94 First Q band −2100 0.75 Second Q band −2000 0.89

TABLE 3 Luminescence lifetimes of Ir(III) corroles in methanol at 298 K;this illustrates that a non-polar solvent such as toluene is notrequired by any means to achieve luminescence in our systems. Compoundτ_(Ar)(μs) [77 K] 1-Ir(tma)₂ 0.103 [2.82] 1b-Ir(tma)₂ 0.668 [3.95 1-Ir(py)₂ 0.470 [7.57]

TABLE 4 Refractive indices (nD²⁰), solvent polarizabilities [f(n)], andIr(III) corrole absorbance maxima (in cm⁻¹) of the solvents used in oursolvatochromic experiments (py = 1-Ir(py)₂, br = 1b-Ir(tma)₂, tm =1-Ir(tma)₂; S1 and S2 = blue and red Soret bands, respectively; Q1 andQ2 = blue and red Q bands, respectively). Solvent n_(D) ²⁰ f (n) pyS1pyS2 pyQ1 pyQ2 brS1 MeOH 1.33 0.169 25674 24528 17244 16202 24894 CH3CN1.34 0.173 25720 24528 17253 16250 24839 Acetone 1.36 0.181 25674 2449217227 16202 24808 Ethanol 1.36 0.181 25634 24474 17227 16194 24857Hexanes 1.37 0.184 25654 24528 17215 16250 24894 THF 1.41 0.199 2556224390 17197 16160 24789 DCM 1.42 0.202 25523 24355 17147 16168 24759 DMF1.43 0.205 25582 24390 17215 16179 24734 CHCl3 1.45 0.212 25465 2430117112 16124 24734 CCl4 1.46 0.215 25465 24278 17109 16145 24808 Benzene1.5 0.227 25465 24254 17138 16098 24734 Toluene 1.5 0.227 25465 2427817138 16108 24734 Pyridine 1.51 0.23 25465 24254 17147 16108 24697Solvent brS2 brQ1 brQ2 tmS1 tmS2 tmQ1 tmQ2 MeOH 23747 17235 15305 2576024438 17535 15723 CH3CN 23702 17235 15256 25786 24390 17516 15708Acetone 23685 17227 15242 25760 24390 17516 15708 Ethanol 23702 1722715316 25740 24390 17516 15723 Hexanes 23764 17253 15434 25813 2445017516 15765 THF 23652 17179 15218 25674 24301 17492 15669 DCM 2363517188 15279 25654 24254 17434 15657 DMF 23618 17188 15218 25674 2430117492 15669 CHCl3 23635 17188 15309 25615 24201 17416 15642 CCl4 2361817206 15366 25634 24143 17391 15635 Benzene 23557 17164 15232 2561524184 17416 15610 Toluene 23557 17164 15232 25634 24201 17434 15635Pyridine 23540 17209 15218 25543 24160 17434 15603

According to embodiments of the present invention, axially ligated five-and six-coordinate iridium(III) corroles have been synthesized and fullycharacterized. Further, the isostructural Group 9 metallocorroles(1-M(PPh₃) and 1-M(py)₂, where M=cobalt(III), rhodium(III), oriridium(III) and 1 denotes the trianion of5,10,15-tris-pentafluorophenylcorrole) have been investigated by X-raycrystallography and cyclic voltammetry. Both chemical andelectrochemical oxidation products have been characterized by absorptionand electronic paramagnetic resonance spectroscopic methods. The averagemetal-N(pyrrole) bond lengths increase from Co (1.886 Å) to Rh (1.957Å)/Ir (1.963 Å); and the average metal-N(pyridine) bond lengths alsoincrease from Co (1.995 Å) to Rh (2.065 Å)/Ir (2.059 Å). There is asurprising invariance in the first reduction potentials within the five-and six-coordinate corrole series, and even between them; the averagehalf-wave potential of 1-M(PPh₃) is 0.78 V vs. Ag/AgCl in CH₂Cl₂solution, whereas that of 1-M(py)₂ is 0.70 V under the same conditions.These Group 9 metallocorroles exhibit dramatically different absorptionspectral changes upon chemical or electrochemical oxidation in CH₂Cl₂solutions, indicating striking differences in electronic structures.Electronic structural variations have been assigned by analysis of EPRspectroscopic measurements on chemically oxidized 1-M(py)₂ corroles. Theg tensor is isotropic for 1-Co(py)₂ (2.006); for 1-Rh(py)₂, g_(∥)=2.032,g_(⊥=)2.001, g_(av)=2.016; for 1-Ir(py)₂, g_(zz)=2.044, g_(yy)=1.993g_(xx)=1.836, g_(av)=1.958: oxidation is corrole-centered for 1-Co(py)₂;corrole-metal delocalized for 1-Rh(py)₂; and primarily metal-centeredfor 1-Ir(py)₂. There also is a clear trend in ligand substitutionbehavior within the Group 9 metallocorroles: ligand affinities at the1-M(PPh₃) open coordination sites differ by three to four orders ofmagnitude in the order 1-Co(PPh₃)<1-Rh(PPh₃)<1-Ir(PPh₃).

According to embodiments of the present invention, corroles of 1-Ir(py)₂and 1-Ir(PPh₃) have been synthesized and characterized, and theirproperties have been compared with those of isoelectronic andisostructural cobalt(III) and rhodium(III) analogs 1-Co(py)₂, 1-Rh(py)₂,1-Co(PPh₃), and 1-Rh(PPh₃) (Scheme 5). This series represents quite arare example of an entire transition metal group of complexes with thesame oxidation state and coordination number. Another group thatfulfills these conditions is comprised of the (por)M-CO complexes ofGroup 8 transition metals. The substitutional lability of the Group 9metallocorroles and the sites of oxidation reactions have beeninvestigated, revealing that both variables change significantly withinthe group. According to spectroelectrochemistry, EPR, and UV-visiblespectroscopic data it appears that: cobalt(III) corroles may besubstitutionally labile compared to either Rh(III) derivatives orIr(III) corroles of the present invention; the affinity of 5-coordinatederivatives for a sixth ligand increases dramatically down the row; andoxidation occurs unambiguously on the metal rather than on the corroleonly in the case of iridium (i.e., Ir(III/IV)).

The electronic spectra of the 6-coordinate cobalt(III) and rhodium(III)corroles are quite similar to one another, while those of theiridium(III) complexes are significantly different (FIG. 14). 1-Co(py)₂and 1-Rh(py)₂ display one major Soret band with almost the same X_(max)and two Q bands at about 580 and 600 nm, while 1-Ir(py)₂ displays ahighly anisotropic Soret band and its Q bands are red-shifted by about20 nm compared to those of the 3d and 4d complexes. It should be notedthat 1-Co(py)₂ is in equilibrium with the mono-pyridine complex 1-Co(py)in CH₂Cl₂ solution [which is not the case for 1-Rh(py)₂ or 1-Ir(py)₂],and this latter species is responsible for the split Soret in thespectrum below. The spectrum of 1-Co(py)₂ in 5% pyridine (where only thebis-ligated form exists in solution) appears in FIG. 15 (at the top) andFIG. 34. As the primary components of the electronic spectra arecorrole-based π-π* transitions in all cases, the differences may beattributed to more significant mixing of MLCT transitions in the orderCo<Rh<Ir. Red shifted Q bands are also exhibited by the 5-coordinate1-Ir(PPh₃), while the Soret bands differ very much within the series:1-Co(PPh₃) has a highly split Soret band, 1-Rh(PPh₃) displays lesssplitting but is red-shifted, and 1-Ir(PPh₃) shows a single, broad Soretband.

The structures of 1-Ir(tma)₂ 1b-Ir(tma)₂ and 1-Ir(py)₂ have beencompared with the structures of 1-Co(py)₂ and 1-Rh(py)₂ analogues. Themain structural features of 1-Ir(py)₂ are: a very planar macrocyclicframework with a root-mean-square atomic deviation of 0.04 Å out of theplane defined by the N4 coordination core; an in-plane metal ion; andtwo essentially parallel pyridine rings (FIG. 16). The informationcompiled in Table 5 allows for a comparison of the metal-nitrogen bondsin 1-Ir(Py)₂, 1-Co(py)₂, and 1-Rh(py)₂. The smaller cobalt(III) ionturns out to form considerably shorter bonds with both the corrole andthe pyridine nitrogen atoms, while the differences between therhodium(III) and the iridium(III) ions are not as great. The somewhatshorter Rh—N(pyrrole) bonds are consistent with the smaller ionic radiusof rhodium(III) relative to iridium(III), while the shorterIr—N(pyridine) bonds indicate that iridium(III) is a stronger Lewis acidthan rhodium(III) within the coordination environment of the corrole.

TABLE 5 Comparison of metal-nitrogen bond lengths (Å) in 1-Co(py)₂,1-Rh(py)₂, and 1-Ir(py)₂. M-N(corrole) M-N(pyridine) 1-Co(py)₂1.873(4)-1.900(4) 1.994(4)-1.995(4) 1-Rh(py)₂ 1.938(5)-1.976(5)2.060(5)-2.071(5) 1-Ir(py)₂ 1.947(2)-1.979(2) 2.052(2)-2.066(2)

1-Co(PPh₃) and 1-Rh(PPh₃) undergo different chemical reactions withpyridine: ligand substitution and addition to form 1-Co(py)₂ in theformer case and addition only as to form 1-Rh(PPh₃)(py) in the lattercase. The 1-Ir(PPh₃) complex behaves similarly to the rhodium(III)analog in this sense, i.e., addition of pyridine leads to a mixed-ligandcomplex. The substitutional lability of the cobalt(III) corrole isfurther exemplified in FIG. 15 (at the top), which shows that additionof PPh₃ to 1-Co(py)₂ leads to 1-Co(PPh₃) and that the former isre-formed upon addition of pyridine to the latter [notice that thespectrum changes slightly due to the elimination of any significant1-Co(py) under excess pyridine]. Complementary information was obtainedvia the examination of spectral changes upon the addition oftriphenylphosphine to the 5-coordinated metallocorroles. While additionof even a 100.000-fold excess of triphenylphosphine induced only minorchanges in the spectrum of 1-Co(PPh₃), the major spectral changes of1-Rh(PPh₃) (FIG. 15, middle) and 1-Ir(PPh₃) (FIG. 15, bottom) werecomplete after the addition of 6300 and 350 equivalents, respectively.The similarity of the visible spectra obtained upon addition oftriphenylphosphine to 1-Rh(PPh₃) and 1-Ir(PPh₃) to those of 1-Rh(py)₂and 1-Ir(py)₂, respectively, suggest that PPh₃ addition to the formercomplexes produces the six-coordinate bis-triphenylphosphine species1-Rh(PPh₃)₂ and 1-Ir(PPh₃)₂. While various corrolato-chelated metal(III)ions have been observed to possess surprisingly low affinity for a sixthligand, these results demonstrate that this effect becomes much lesspronounced upon moving downwards within the periodic table. This may beattributed to the stronger Lewis acidity of 4d and especially 5d metalions, such that coordination of a sixth σ-donating ligand becomes muchmore favorable moving down the group. This phenomenon plays a role inunderstanding the results presented in the following sections.

Electrochemistry. Investigation of the differences between theβ-pymmole-unsubstituted complex 1-Ir(tma)₂ and its fully brominatedanalog 1b-Ir(tma)₂ reveals that the latter displays one oxidation andone reduction within the solvent potential window of CH₂Cl₂, while noreduction and two reversible oxidations were observed for the former.The first positive redox potentials of the complexes might reflecteither metal-centered (M(III)/M(IV), where M=Co, Rh, or Ir) orligand-centered (tpfc/tpfc⁺) processes. The cyclic voltammograms of allcomplexes are shown in FIG. 17, while Table 6 lists the correspondinghalf-wave potentials. The results reveal that the 6-coordinated 1-M(py)₂complexes are oxidized at lower potentials than the 5-coordinated1-M(PPh₃) complexes and that the difference becomes smaller in the orderof Ir<Rh<Co. The most surprising result is the very small difference inredox potentials for the differently metallated compounds: 0.70±0.03 for1-M(py)₂ and 0.78±0.06 for 1-M(PPh₃). A metal-based process(M^(III)/M^(IV)) throughout the series may be ruled out because of thevery large effects that would be expected in such a case, as may beexemplified by the 0.2-0.3 V more positive redox potentials of theRh^(III/IV) couple relative to the Ir^(III/IV) couple in cyclometalatedcomplexes. On the other hand, the central metal ion should have apronounced effect even if the macrocycle is oxidized, as has beenobserved for both corroles and porphyrins. This emphasized the need fora more detailed investigation of the processes, which was performed viaspectroscopic examination of the oxidation products.

TABLE 6 Redox potentials (CH₂Cl₂, TBAP, vs. Ag/AgCl) for the firstoxidation processes of the Group 9 metal(III) corrole complexes. Underidentical conditions, the E_(1/2) for ferrocene was 0.55 V; and iodinedisplayed an E_(pa) of 0.89 V and an E_(pc) of 0.39 V. 1-M(PPh₃)₂E_(1/2) 1-M(py)₂ E_(1/2) M = Co 0.83 M = Co 0.67 M = Rh 0.79 M = Rh 0.72M = Ir 0.72 M = Ir 0.71

Visible spectroscopy of the one-electron-oxidized metal(III) corroles:Changes in the electronic spectra upon oxidation were used as a tool foranalyzing whether the metal or the corrole is the center of the redoxreactions, relying on two different chemical oxidants (iodine and t-4bpa) and spectroelectrochemistry. The advantage of using moleculariodine is that it should not be able to induce double oxidation (Table6), while the t-4bpa cation is a good choice of oxidant because (unlikeiodine) its reduced products do not interact with the metal center.One-electron oxidation of 1-Co(PPh₃) and 1-Rh(PPh₃) by either iodine(FIGS. 31 and 32) or t-4bpa (FIG. 18) induced a significant reduction ofthe intensity of the original Soret and Q bands and the formation of anew broad band that appears at 690 nm (∈=4000) for the cobalt complexand at 710 nm (∈=2300) for the rhodium complex. These characteristicsare consistent with corrole-centered oxidation, i.e., formation ofcorrole radicals. Despite their less positive redox potentials, thesix-coordinate complexes 1-Co(py)₂ and 1-Rh(py)₂ seemed inert to iodineoxidation, but could still be oxidized with t-4 bpa (FIG. 19). Theindications for formation of corrole radicals upon oxidation are evenstronger in these complexes than in the five-coordinate cases, as thenew bands at long wavelength are more pronounced and the Soret bandsundergo small hypsochromic shifts.

The spectral changes upon oxidation of the iridium(III) corroles aresignificantly different from those of their 3d and 4d analogs. Oxidationof 1-Ir(PPh₃) by iodine results in a severe decrease in the intensity ofthe Soret band, accompanied by splitting and broadening, as well asalmost complete disappearance of the Q bands. Concomitantly, two newabsorption bands arise at and above 700 nm, of which the more intenseone, at 840 nm (∈=5000), may be assigned as an LMCT transition from thecorrole to a newly formed iridium(IV) center. Oxidation of the samecomplex by t-4 bpa instead of iodine results in two distinct oxidationprocesses with their own sets of isosbestic points (FIGS. 20 a and b).The first process, which appears to occur with near exclusivity up toabout 0.6 equivalents of t-4 bpa, results in a less intense Soret band,the total disappearance of any Q-band structure, and the rise of smallbands at 695 nm (E=2800) and 821 nm (∈=2000). One important aspect ofthe spectral changes is that the Soret band of singly oxidized1-Ir(PPh₃) strongly resembles those of the six-coordinate iridium(III)corroles 1-Ir(py)₂ (FIG. 14, top) and 1-Ir(PPh₃)₂ (FIG. 15, middle). Thesecond process results in the rise of a weak, bathochromically shiftedSoret band at 460 nm (∈=30000) coincident with the growth of a newQ-band at 580 nm (∈=5700) as well as a red-shifted and more intense LMCTband at 833 nm (∈=4500). In contrast with 1-Ir(PPh₃), but similarly tothe cases of 1-Co(py)₂ and 1-Rh(py)₂, 1-Ir(py)₂ seems not to react withiodine according to visible spectroscopy. Its oxidation by t-4 bpareveals isosbestic points up when up to 1.1 equivalents of oxidant areused, leading to a spectrum that displays diminished Soret and Q bandsand new bands with about equal intensity at 683 and 793 nm that seemsimilar to the LMCT bands observed in the spectra of oxidized 1-Ir(PPh₃)(FIG. 20 c). Larger amounts of t-4 bpa were used as well, but this ledto an uninterpretable spectrum, possibly due to decomposition of thecorrole. The different results obtained with iodine vs. t-4 bpa as anoxidant for the two types of complexes, as well as the apparent changesthat occur during oxidation of the iridium(III) corroles by even lessthan one equivalent of t-4 bpa, were investigated byspectroelectrochemistry.

The changes in the visible spectrum of 1-Ir(PPh₃) were examined at 1.0V, which is high enough to assure full oxidation, but low enough toavoid double oxidation. Nevertheless, two complexes are clearly formed(FIG. 31): the first, with a new band at 811 nm and a relatively simpleSoret band, is later transformed into a species whose Soret band isheavily split, which has a new Q band at 580 nm, and which displays alow energy band at 844 nm (FIG. 31, inset). These results confirm theproposed mechanism of chemical oxidation, as virtually identical changeswere observed for the combination of 1-Ir(PPh₃) with t-4 bpa. The firstband that appears at 811 nm clearly represents the one-electronoxidation product, but the initial product is clearly unstable: ittransforms into a new molecular species even when a second oxidation isarrested by either controlling the electrochemical potential or byadding less than one equivalent of chemical oxidant. The similarity ofthe final Soret band obtained upon both chemical and electrochemicaloxidation of 1-Ir(PPh₃) to those of 6-coordinated iridium(III) corrolesseems to suggest that the apparent instability of the initial oxidationproduct is due to the increased ligand affinity of iridium(IV),resulting in binding of a sixth ligand from the electrolyte, the oxidantor solvent impurities.

The above hypothesis regarding the apparent instability of theone-electron oxidation product was examined by performing thespectroelectrochemistry of 1-Ir(PPh₃) in the presence of 5 equivalentsof PPh₃ (FIG. 22). This resulted in an almost perfectly clean conversionto the final product obtained in the absence of PPh₃, thus indicatingthat the initially formed complex has a large affinity for a sixthligand and becomes much more stable when it is supplied. All the resultsare consistent with expectations for a genuine iridium(IV) complex,which would not necessarily display significant changes in the Soretband unless its coordination number changes, but should have increasedaffinity for a sixth ligand and show an LMCT transition at above 800 nm.

EPR spectra of oxidized iridium(III) corroles. Both organic radicals andd⁵ iridium ions are paramagnetic, S=½ systems, but EPR spectroscopy canalmost always be used to distinguish between the two. Carbon-centeredorganic radicals, such as that of H₃tpfc or its gallium(III) complex,tend to have g tensor values very close to the free electron value ofg=2.0023, with little hyperfine coupling and no g tensor anisotropy. Onthe other hand, iridium(IV) compounds display highly anisotropicsignals, often accompanied by hyperfine couplings to the metal nucleusand/or other EPR-active nuclei.

In order to facilitate characterization of their singly oxidized forms,complexes 1-Co(py)₂, 1-Rh(py)₂, and 1-Ir(py)₂ were oxidized chemically,and their EPR spectra were then recorded in frozen toluene solutions.With t-4 bpa as oxidant, the spectrum of the oxidized cobalt complexdisplays one narrow band centered at g=2.006 (FIG. 23 a), clearlyindicating that this species is a delocalized corrole radical. Theoxidized rhodium complex displays a broader line with some additionalfeatures in its EPR spectrum (FIG. 23 b), which can best be modeled as alargely corrole-based radical with moderate spin density on the rhodiumnucleus (g_(∥)=2.032, g_(⊥)=2.001, g=2.016). Similar results, i.e., bothpure corrole radicals and metal-coupled corrole radicals, have beenpreviously observed for high valent cobalt corroles and corrolazines(5,10,15-triazacorroles). A more uncommon result was obtained in thecase of the six-coordinated iridium(III) corrole. Iodine, though notproducing UV-vis spectral changes upon its addition to 1-Ir(py)₂, wasused in the EPR experiments in order to confirm the hypothesis that itnevertheless affects oxidation. Addition of iodine to a toluene solutionof the corrole (FIG. 23 c) results in a highly rhombic spectrum(g_(zz)=2.044, g_(yy)=1.993 g_(xx)=1.836, g=1.958) that is clearlyinconsistent with oxidation centered on the corrolato ligand. On theother hand, the spectrum is very similar to those of low-spin d⁵metalloporphyrinoids such as bis-amine-iron(III) porphyrins and(tpfc)Fe(py)₂, the bis-pyridine-iron(III) complex of the same corrolethat was utilized in the current studies. These data indicate that thefirst oxidation process in 1-Ir(py)₂ occurs at the metal, resulting inan iridium(IV) complex. Meanwhile, the cobalt corrole becomes anunambiguous organic radical upon oxidation, and the rhodium complexdisplays an EPR spectrum consistent with a highly coupled organicradical system.

The EPR results from oxidation of the five-coordinate complexes[1-Co(PPh₃), 1-Rh(PPh₃), and 1-Ir(PPh₃)] were less straightforward dueto apparent problems with decomposition and/or binding of oxidants,although the spectra of singly oxidized cobalt and rhodium corroles arequite similar to those of their hexacoordinate analogs. Much moreambiguous results were obtained for the (triphenylphosphine)iridium(III)corrole complex, compounding the evidence that the oxidized form of1-Ir(PPh₃) undergoes chemical reactions due to increased affinity for asixth ligand upon oxidation.

The investigation of the reactivity patterns of an isostructural seriesof transition metal corroles is highly illuminating in terms of chemicalreactivity and the stability of high oxidation states. There is a cleartrend within the series in terms of ligand substitution (onlycobalt(III) corroles undergo it at room temperature) and ligand addition(Co<Rh<Ir), while all complexes display virtually identicalelectrochemical redox potentials. The unexpected insensitivity of theoxidation potentials to the metal ions has been resolved for thesix-coordinated complexes by invoking different centers of oxidation foreach complex. Spectral data demonstrate that the first oxidation iscorrole-centered for cobalt, corrole-based with some metal contributionfor rhodium, and metal-centered for iridium. Regarding thefive-coordinate complexes, the results imply that these compoundsincrease in affinity for a sixth ligand by three to four orders ofmagnitude as one moves from cobalt to rhodium and then to iridium. Theseresults indicate that iridium corroles behave very differently fromtheir 3d and 4d analogs.

The electronic structures of metallocorrole complexes(tpfc)M^(III)(NH₃)₂, where tpfc is the anion of5,10,15-(tris)pentafluorophenylcorrole and M=Co, Rh, Ir) have beencomputed by DFT methods (B3LYP with Poisson-Boltzmann continuumsolvation). In each case, one-electron oxidation is calculated to occurfrom a ligand-based orbital (HOMO of B₁ symmetry). Variations in thecalculated M(IV/III) reduction potentials (0.64, 0.67, and 0.56 V vs SCEfor M=Ir, Rh and Co, respectively) are small compared to expectation formetal-based oxidations. Excited states with substantial metal characterare well separated from the ground state in the one-electron-oxidizedcobalt corrole.

Electronic structure calculations may provide insight into the factorsthat determine the stability and reactivity of metal complexes in highoxidation states and could in principle facilitate the design ofcatalysts for substrate oxidation reactions. One issue that suchcalculations may address is that the metal-chelating ligands themselvesoften undergo redox changes during catalysis. Such noninnocent ligandbehavior may be a hallmark of oxidative catalytic cycles of hemeenzymes, where a highly reactive intermediate formed by two-electronoxidation of an iron(III) precursor is better described as anoxoiron(IV) ligand radical than as an iron(V) complex. Depending on theparticular enzyme, one unpaired electron is located on either an orbitalof the chelating porphyrin or on a nearby amino acid residue. Notably,advances in synthesis, together with high level spectroscopy and theory,have continued to provide insights into these and related issues, withsurprising findings in certain cases: for example, the likelihood of arole for electronic excited-state coupling in promoting catalytichydroxylations by heme and nonheme-iron enzymes.

The successful syntheses of five- and six-coordinate iridium(III)corroles completed a very rare isostructural 3d (Co^(III)), 4d (R^(III))and 5d (Ir^(III)) series, and prompted the development of electronicstructural descriptions of analogous 3d-4-d-5d Group 9 metallocorroles.Surprisingly, the measured redox potentials show slight variation amongthe three corroles, while EPR results suggest a shift from corrole- tometal-centered oxidation in moving from 3d and 4d to 5d complexes. Inparticular, electronic structure calculations may provide an explanationfor the small differences in Co(IV/III), Rh(IV/III) and Ir(IV/III)reduction potentials, and the greatly enhanced metal character indicatedby EPR experiments in going from “Rh(IV)” to “Ir(IV)”.

Density functional theory (DFT) was used for the determination ofmetallocorrole electronic structures. The structural parameters of(tpfc)Ir(NH₃)₂ (tpfc=5,10,15-tris-pentafluorophenylcorrole) from thecalculation are consistent with those obtained from X-ray diffractioncrystallographic measurements. Calculations were made of the redoxpotentials as well as the electronic structures of[(tpfc)M(NH₃)₂]^(0/+). Additionally, less computationally taxing[(tfc)M(NH₃)₂]^(0/+) (tfc=5,10,15-trifluorocorrole) models wereexamined. Of special interest is that computational results show thatthe very small nd (n=3,4,5) dependence of the reduction potentials ofGroup 9 metallocorroles is accompanied by a marked decrease in metalorbital energies (compared with those of the corrole) in the order 3d to4d to 5d.

All computations were conducted with the Jaguar 7.0 package (release207), applying the hybrid density functional B3LYP. Although no singlefunctional has been shown to be superior for applications tospectroscopy, magnetic properties and transition metal thermochemistry,B3LYP has proved useful in the calculation of oxidation potentials andyielded spin density distributions and excited state orderings similarto CASPT2 results for an iron-heme model. Free energies used in thecalculation of oxidation potentials are equal to:G=E _(el,gas) +G _(solv) +ZPE+H _(vib) −S _(vib) Twhere E_(el,gas) is the gas phase electronic energy, G_(solv) is thesolvation energy of the compound in dichloromethane, ZPE is thezero-point energy of the complex, H_(vib) is the vibrational enthalpy,and S_(vib) is the vibrational entropy. The temperature was set to 298 Kfor all calculations. Geometries were optimized and hessians forvibrational spectra were calculated in vacuum using the Los Alamoseffective core potential with 2-ζ valence functions for the metals and6-31G** for all other atoms. Single point energies were then calculatedusing a 3-ζ contraction of the Los Alamos valence functions augmentedwith two f-functions for metals and 6-311G**++ for other atoms.Solvation energies were obtained at the vacuum-optimized geometries withthe Poisson-Boltzmann continuum solvation model using a dielectricconstant of ∈=8.93 and probe radius of 2.33 Å to representdichloromethane. The oxidation potentials (in V) relative to thestandard hydrogen electrode (SHE) were calculated according to theequationE _(SHE)=(G _(ox) −G _(red))/(N _(el))(23.06 kcal/mol·eV)−4.29V,and the corresponding potentials relative to the saturated calomelelectrode (SCE) areE _(SCE) =E _(SHE)−0.24V,where G_(ox) is the Gibbs free energy (in kcal/mol) of the oxidized formof the complex and G_(red) is that of the reduced form.

To simplify orbital analysis of excited states, geometries of the(tpfc)M^(III)(NH₃)₂ and (tfc)M^(III)(NH₃)₂ complexes were optimized withC_(2v) symmetry enforced. Then, single point energy calculations usingthe 2-ζ basis were performed on the corresponding “M(IV)” complexes toobtain the energies of various states with the electron taken fromdifferent orbitals of the M(III) complexes. Level-shifting was appliedto aid convergence of the excited states. The spin densities and chargeson the metals were also obtained through Mulliken analysis. Unlessotherwise stated in the text, upper-case symmetry labels (e.g. ¹A₂)denote excited states with the electron ionized from an orbital of thecorresponding symmetry. The orbitals themselves are denoted bylower-case symmetry labels (e.g. ¹a₂).

The crystal structure of (tpfc)Ir(NH₃)₂ shows a quasi-C2v symmetryaround the metal center with the principal axis passing through Ir andC15 (FIG. 38). The experimental Ir—N(ammine) bond lengths are 2.074 Åeach, and the average Ir—N(pyrrole) bond length is 1.964 Å. The computedIr—N(ammine) and Ir—N(pyrrole) bond length are, respectively 2.112 and1.976-1.996 Å, in good agreement with the crystallographic data.Dihedral angles of the pentafluorophenyl groups in vacuum-optimizedstructures were 66-76 degrees. The energy change caused by rotation ofthe pentafluorophenyl groups away from perpendicular averages 0.03 eV,which is on the same order of magnitude as the uncertainty in energycomputations. This small energy penalty is consistent with dihedralangles in practically all triarylcorrole structures.

The computed increases in the length of the bonds C10-C11 and C6-C24Table 7) upon removal of an electron from the neutral complexes areconsistent with the description in a previous publication of bond lengthchanges upon formation of a corrole-based cation radical of B symmetry.Changes in both types of metal-nitrogen bond lengths (M-N_(pyrrole) andM-NH₃) are much smaller, suggesting that the oxidation state of themetal stays the same upon removal of one electron from these complexes.

TABLE 7 Key bond lengths of [(tpfc)M(NH3)2]0/+, for M = Co, Rh, and Ir.The number in parenthesis following the atomic symbol of the metal isthe formal oxidation state of the metal in the corresponding complex,i.e., considering the corrole ligand as non-oxidized. tpfc Co(III)Co(IV) delta Rh(III) Rh(IV) delta Ir(III) Ir(IV) delta M-N66 1.988 1.9950.007 2.107 2.114 0.007 2.112 2.119 0.007 M-N70 1.987 1.992 0.005 2.1082.116 0.008 2.112 2.120 0.008 Average 1.988 1.994 0.006 2.108 2.1150.007 2.112 2.120 0.008 M-N (NH3) M-N2 1.887 1.888 0.001 1.967 1.9680.001 1.976 1.976 0.000 M-N3 1.916 1.913 −0.003 1.993 1.991 −0.002 1.9971.996 −0.001 N2-C6 1.37 1.356 −0.014 1.369 1.355 −0.014 1.371 1.356−0.015 N2-C9 1.36 1.371 0.011 1.356 1.365 0.009 1.36 1.367 0.007 N3-C111.386 1.373 −0.013 1.38 1.368 −0.012 1.383 1.37 −0.013 N3-C14 1.3711.375 0.004 1.365 1.369 0.004 1.368 1.371 0.003 C6-C24 1.425 1.442 0.0171.446 1.466 0.020 1.45 1.471 0.021 C9-C10 1.414 1.401 −0.013 1.428 1.414−0.014 1.429 1.415 −0.014 C10-C11 1.408 1.431 0.023 1.422 1.447 0.0251.425 1.449 0.024 C14-C15 1.410 1.414 −0.004 1.424 1.428 −0.004 1.4261.429 −0.003

As expected, the ground state of [(tpfc)Ir(NH₃)₂] displays six dπelectrons and a closed-shell corrole π-system (FIG. 39). In the groundstate of [(tpfc)Ir(NH₃)₂]⁺, the d⁶ configuration on Ir remains intactwhile the 1b₁ orbital of the corrole is singly occupied. There iseffectively no spin density on the metal, and the atomic charge of Irfrom Mulliken population analysis remains essentially constant (0.87 to0.89). Co and Rh present similar features.

The relative energies as well as the metal spin densities of excitedstates of [(tpfc)M(NH₃)₂]⁺ are compared in Table 8. The spin densityplots in FIG. 40 show that the higher-energy excited states for eachmetal, particularly for iridium, contain significant metal character.Although the pentafluorophenyl group (C₆F₅) was the meso-substituentused in experiments, the imaginary [(tfc)M(NH₃)₂]⁺ complexes were alsocalculated because simpler meso-substituents greatly reduce the timerequired for computation. The tpfc complexes also often ended up on asaddle point due to a shallow potential energy surface caused byrotation of the C₆F₅ groups. Parameters for the tfc complexes can befound in Table 9, and the spin density surfaces and energy levels ofthese complexes can be viewed in FIG. 41.

TABLE 8 Spin densities and energies of the excited states of the tpfccomplexes. The symmetry label of the state is the symmetry of theorbital from which the electron has been ionized. Relative energy is theenergy of the state in question minus that of the lowest energy ionizedstate of the same compound. Metal spin density represents the spindensity on the metal, in total unpaired electron spins. There are otherstates with the unpaired electron on corrole-based orbitals between 2B₁and 1A₁ for Rh and Co. Co Rh Ir Relative Relative Relative tpfc energyMetal spin energy Metal spin energy Metal spin State (eV) density (eV)density (eV) density 1B₁ 0.00 −0.02 0.00 −0.01 0.00 −0.01 1A₂ 0.27 0.000.24 0.02 0.15 0.07 2A₂ 1.63 0.10 1.23 0.21 0.59 0.08 2B₁ 1.71 0.12 1.270.24 0.86 0.38 1A₁ 2.74 1.13 2.71 0.75 2.06 0.89

TABLE 9 Spin densities and energies of the excited states of the tfccomplexes. The symmetry label of the state is the symmetry of theorbital from which the electron has been ionized. Relative energy is theenergy of the state in question minus that of the lowest energy ionizedstate of the same compound. Metal spin density represents the spindensity on the metal, in total unpaired electron spins. There are otherstates with the unpaired electron on corrole-based orbitals between 3B₁and 1A₁ for Rh and Co. Co Rh Ir Relative Relative Relative tfc energyMetal spin energy Metal spin energy Metal spin State (eV) density (eV)density (eV) density 1B₁ 0.00 −0.02 0.00 −0.01 0.00 −0.01 1A₂ 0.67 0.000.63 0.02 0.54 0.07 2A₂ 1.94 0.08 1.58 0.19 1.21 0.24 2B₁ 2.02 0.10 1.620.22 1.21 0.35 3B₁ 2.33 −0.01 2.28 0.00 2.27 0.00 1A₁ 3.19 1.16 3.190.77 2.53 0.91

From observation of the energy levels in both the tpfc and the tfcsystems, it is apparent that the dispersion between states decreases inthe order Co>Rh>Ir for each corrole system. Also, it is noteworthy thatthe spin density localized on the metal generally increases in the orderCo<Rh<Ir for a given orbital level, except for the high-lying 1A₁ state,which is in the order Rh<Ir<Co. States classified as 3B₁ only appear inthe tfc complexes because they are pushed upward in energy when theligand is tpfc. FIG. 41 shows that the energy of the 3B₁ state relativeto the 1B₁ state in the three tfc complexes is roughly the same for allthree metals.

For a given metal center, the tpfc complex has smaller energy gapsbetween different states than the tfc complex. An exception is the gapbetween the nearly degenerate 2B₁/2A₂ states and the adjacent 1A₂ state,which is actually increased by around 0.04 eV in the tpfc case due tostabilization of the 1A₂ state by the pentafluorophenyl substituents ontpfc. The contraction observed between the lowest two energy states forthe different corrole ligands is of a greater order than the differencebrought about by changing the metal center for each corrole, presumablybecause the ground 1B₁ state is more effectively stabilized by fluorinethan by pentafluorophenyl meso-substituents. [(tpfc)Ir(NH₃)₂]⁺ has thesmallest dispersion of all compounds under study, such that the energygap between the 1B and 1A₂ states is only approximately 0.15 eV invacuum, dropping to 0.10 eV if dichloromethane solvation is added to themodel. Solvation with dichloromethane decreases dispersion in a generalfashion.

The calculated reduction potential of [(tpfc)Ir(NH₃)₂]^(0/+) accordswith the experimental value (0.53V vs. SCE) obtained via cyclicvoltammetry. The computed reduction potentials of [(tpfc)M(NH₃)₂]^(0/+)are 0.64, 0.67, and 0.56 V vs. SCE for M=Ir, Rh, and Co, respectively.

These DFT calculations point toward a common description of thepositively charged cobalt, rhodium and iridium corroles as metal(III)complexes chelated by an oxidized, open-shell corrole macrocycle, withan unpaired electron that resides in a corrole-based B₁ symmetryorbital. Nevertheless, there are significant differences between the twoinvestigated corrole ligands. For a given metal center, substitution byC₆F₅ as opposed to F at the meso-positions decreases the energeticdifference between the vertically excited states of the cations. Thisenergetic dispersion is also strongly affected by the metal, in theorder of Co>Rh>Ir. The effect of the metal center and that of themeso-substituents on the energetic states of the system are largelydecoupled for the rhodium and cobalt complexes. However, in the case ofiridium, the excited tfc complex has degenerate energetic states(2B₁/2A₂) that become nondegenerate in the corresponding tpfc complex.

Without being limited by theory, the remarkable effects that themeso-substituents have on the energy levels of the corrole complexes maybe rationalized by the following arguments: While pentafluorophenyl is apoorer electron-withdrawing group (EWG) than fluoride regarding itsinductive effect, the inductive electron-withdrawing effect of thelatter substituent is mitigated by its ability to donate electrondensity from filled fluorine 2p orbitals into the π-system of thecorrole, resulting in an overall greater electron-withdrawing effect ofthe C₆F₅ substituent on the electronic structure of the corrole complex.This is confirmed by the fact that the bonds immediately adjacent to thefluorine are shorter than the corresponding bonds in tpfc, but the bondsfarther away from the meso substituents are similar in the two corrolescaffolds. The contraction of energy dispersion implies thatpentafluorophenyl is more capable of lowering the energy of those statesthat have a high percentage of metal character than of stabilizing thosethat have more corrole character. There is also a computed contractionof energy dispersion upon moving from Co to Rh to Ir, and the combinedeffects of having a C₆F₅ meso-substituent and the 5d metal ion in[(tpfc)Ir(NH₃)₂]⁺ leads to a situation where the 1A₂ state (which hassignificant unpaired spin density on the metal ion) is as little as 0.1eV above the lowest energy B₁ state when solvation effects are included(or 0.15 eV in vacuum).

Without being limited by theory, these observations help to explain theexperimental finding of increased metal character in singly oxidized(tpfc)M^(III)(NH₃)₂ complexes going from Co to Rh to Ir, especially whenthe general trend that spin-orbit coupling increases down a Group isadded to the analysis. Addition of spin-orbit effects into the DFTmodels would require computationally intensive valence-bondconfiguration interaction calculations, but given that spin-orbitcoupling in 5d metals is known to be on the order of nearly half an eV,the 1A₂ state of [(tpfc)Ir(NH₃)₂]⁺ could easily drop lower in energythan the 1B₁ corrole π-cation state. In fact, the experimental EPRspectrum of [(tpfc)Ir(NH₃)₂]⁺ displays rhombic splitting of the g-tensorthat can only arise if significant metal character is mixed into theground state. For cobalt and rhodium, on the other hand, the energydifference between the 1A₂ and 1B₁ states is larger than for iridium andmoreover spin-orbit effects on the 1A₂ states of the 3d and 4d corrolesare likely to be negligible.

The calculated reduction potentials are very similar among the series of[(tPfc)M(NH₃)₂]^(0/+) redox pairs. Considering the fact that oxidationof the M(III) corrole complexes always involves ionization of oneelectron from the HOMO, calculated to be a pure corrole orbital, withoutbeing limited by theory, there might be two explanations for thisphenomenon. It is possible that the metal centers simply have very minoreffects on the energy of the corrole-based HOMO of each complex becauseof poor orbital overlap, leading to the computed result that theirenergies (and therefore their reduction potentials) are the sameregardless of the metal center. It seems that the metal center wouldperturb the energy levels of the corrole orbitals by providing analtered electric field regardless of orbital interaction, and that thedifferences among the effective electronic shielding of each metal wouldlead to large changes in the reduction potentials of the complexes.However, only fairly minor differences are observed among the computedreduction potentials of the three Group 9 corrole complexes, consistentwith experimental data.

DFT calculations (B3LYP with Poisson-Boltzmann continuum solvation)applied to the series of Group 9 metallocorrole complexes(tpfc)M^(III)(NH₃)₂ (M=Co, Rh, Ir) and the corresponding cations predicta common, ligand-based one-electron oxidation in each case.Wavefunctions for the neutral M(III) molecules share a HOMO of B₁symmetry with insignificant contribution from the metal, andlowest-energy wavefunctions for the cations yield spin densities withlittle contribution (˜0.01 electron) from the metals. Calculatedoxidation potentials (0.64 V, 0.67 V, and 0.56 V vs. SCE for M=Ir, Rhand Co, respectively) appear to be insensitive to the metal within theaccuracy of the calculation, and are consistent with the measuredoxidation potential of [(tpfc)Ir(NH₃)₂]^(0/+) (0.53 V vs. SCE).

In the cations, however, vertical excitation energies to states withsignificant metal character decrease in the order Co>Rh>Ir, and are aslow as 0.15 eV in (tpfc)Ir(NH₃)₂ ⁺. Spin-orbit coupling, omitted in thecalculations at this level of theory, could conceivably mix thelow-lying states incorporating Ir d_(xz) and d_(yz) character to yield amixed metal-ligand radical ground state as the experimental evidencesuggests.

TABLE 10 Generated excited-state orbitals of (tfc)Ir^(III)(NH₃)₂.Symmetry Orbital Resulting Resulting Energy relative of ionized numberin spin atomic to Ir^(IV) ground orbital Ir^(III) density on Ir chargeon Ir state (eV) B₁ 107 −0.01 0.88 0.00 A₂ 106 0.07 0.91 0.54 A₂ 1040.24 0.92 1.21 B₁ 105 0.35 0.97 1.21 B₁ 103 0.00 0.89 2.27 A₁ 102 0.911.18 2.53

TABLE 11 Generated excited-state orbitals of (tfc)Rh^(III)(NH₃)₂.Orbital Spin density on Atomic charge on Relative energy Symmetry numberRh Rh (eV) B₁ 107 −0.01 0.79 0.00 A₂ 106 0.02 0.81 0.63 A₂ 105 0.19 0.841.58 B₁ 104 0.22 0.85 1.62 B₁ 103 0.00 0.80 2.28 A₁ 99 0.77 1.05 3.19

TABLE 12 Generated excited-state orbitals of (tfc)Co^(III)(NH₃)₂.Orbital Spin density on Atomic charge on Relative energy Symmetry numberCo Co (eV) B₁ 107 −0.02 0.48 0.00 A₂ 106 0.00 0.49 0.67 A₂ 105 0.08 0.501.94 B₁ 104 0.10 0.50 2.02 B₁ 103 −0.01 0.49 2.33 A₁ 98 1.16 0.69 3.19

TABLE 13 Generated excited-state orbitals of (tpfc)Ir^(III)(NH₃)₂.Orbital Spin density on Atomic charge on Relative energy Symmetry numberIr Ir (eV) B₁ 215 −0.01 0.88 0.00 A₂ 214 0.07 0.90 0.15 A₂ 212 0.08 0.850.59 B₁ 213 0.38 0.97 0.86 A₁ 211 0.89 1.17 2.06

TABLE 14 Generated excited-state orbitals of (tpfc)Rh^(III)(NH₃)₂.Orbital Spin density on Atomic charge on Relative energy Symmetry numberRh Rh (eV) B₁ 215 −0.01 0.79 0.00 A₂ 214 0.02 0.80 0.24 A₂ 213 0.21 0.841.23 B₁ 212 0.24 0.86 1.27 A₁ 202 0.75 1.04 2.71

TABLE 15 Generated excited-state orbitals of (tpfc)Co^(III)(NH₃)₂.Orbital Spin density on Atomic charge on Relative energy Symmetry numberCo Co (eV) B₁ 215 −0.02 0.47 0.00 A₂ 214 0.00 0.48 0.27 A₂ 213 0.10 0.481.63 B₁ 212 0.12 0.49 1.71 A₁ 201 1.13 0.66 2.74

FIGS. 1-46 show illustrations of emission spectra, nuclear magneticresonance (NMR) spectra, cyclic voltammograms, x-ray diffractioncrystallographic structures, UV-vis spectra, normalized excitationprofiles, Raman spectra, spectroelectrochemical results, electronparamagnetic resonance (EPR) spectra, electrospray ionization massspectrometry (ESI-MS) traces, atom numbering schemes, molecular orbitalsurfaces, relative energies and spin density surfaces, and orbitaldrawings and energies of the various compounds discussed herein. Inparticular, FIGS. 1 and 2 are graphs of emission (phosphorescence)spectra of 1-tma, 2-tma, 1-py and 1-CNpy in CH₂Cl₂ solutions at roomtemperature. FIG. 3 is a graph of a ¹H nuclear magnetic resonance (NMR)spectrum of 1 in CD₂Cl₂ and UV-vis spectra of 1 (red) and 2 (blue) inCH₂Cl₂; inset is a graph of the β-pyrrole proton resonances. FIG. 4 is agraph of cyclic voltammogram (CV) traces of 1-Ir(tma)₂ (in red) and2-Ir(tma)₂ (in blue) in CH₂Cl₂ solution at 23° C. FIG. 5 is anillustration of the X-ray structures of 1 (left) and 2 (right),illustrating: 50% probability displacement ellipsoids; and average bonddistances of: Ir—N (equatorial) 1.965 (9) [1-Ir(tma)₂], 1.974(3)[2-Ir(tma)₂] and Ir—N (axial) 2.185 (9) [1-Ir(tma)₂], 2.189(3)[2-Ir(tma)₂]. FIG. 6 is a graph of emission spectra of Ir(III) corrolesin degassed toluene solution (λ_(ex)=496.5 nm); a. was measured at 298K; b. was measured at 77 K. FIG. 7 is a graph of UV-vis spectra ofIr(III) corroles in toluene solution at 298 K. FIG. 8 is a graphillustrating the shift in the lower energy Soret component as a functionof solvent polarizability (the sodium D line at 20° C. was used for n).FIG. 9 is a graph illustrating spectral shifts of the absorption maximaas a function of solvent polarizability for the weaker Soret and both Qabsorption bands in various solvents. FIG. 10 is a graph of UV-visabsorption spectra of (top to bottom): 1-Ir(tma)₂, 1b-Ir(tma)₂,1-Ir(py)₂ at room temperature in a broad range of solvents; the inset isa graph of the Soret band used for the calculation of the solvatochromicshifts discussed herein. FIG. 11 is a graph of normalized excitationprofiles of (top to bottom): 1-Ir(tma)₂, 1b-Ir(tma)₂, 1-Ir(py)₂monitored at emission wavelengths of 790 and 890 nm. FIG. 12 is a graphof Raman spectra of 1-Ir(tma)₂, 1b-Ir(tma)₂, 1-Ir(py)₂; sampleexcitation into the Soret was achieved with the 488 nm line of an argonion laser. FIG. 13 is a graph of a ¹H NMR spectrum (red) and a graph ofa ¹⁹F NMR spectra (blue inserts) of 1-Ir(py)₂. FIG. 14 is a graph ofelectronic spectra of the 6-coordinate bis-pyridine metal (III) corroles(top) and the 5-coordinate PPh₃-coordinated metal(III) corroles(bottom), at 2.5 μM concentration in CH₂Cl₂. FIG. 15 is a series ofgraphs illustrating the changes in the electronic structure in CH₂Cl₂that demonstrate (from top): the reversible transformations between1-Co(py)₂ and 1-Co(PPh₃) upon addition of PPh₃ and pyridine; formationof 1-Rh(PPh₃)₂ from 1-Rh(PPh₃); and formation of 1-Ir(PPh₃)₂ from1-Ir(PPh₃). FIG. 16 is an illustration of the molecular structure of thebis-pyridine Ir(III) corrole 1-Ir(py)₂ (hydrogen atoms omitted). FIG. 17is a series of graphs of CV traces of CH₂Cl₂ solutions of the 1-M(PPh₃)and 1-M(py)₂ complexes. FIG. 18 is a series of graphs illustratingchanges in the electronic spectra indicating oxidation of 1-Co(PPh₃)(top) and 1-Rh(PPh₃) (bottom) bytris(4-bromophenyl)aminiumhexachloroantimonate (t-4 bpa) in CH₂Cl₂. FIG.19 is a series of graphs illustrating changes in the electronic spectraindicating oxidation of 1-Co(py)₂ (top) and 1-Rh(py)₂ (bottom) by t-4bpa in CH₂Cl₂. FIG. 20 is a series of graphs illustrating changes in theelectronic spectra indicating oxidation by t-4 bpa in CH₂Cl₂ of (fromtop): a) 1-Ir(PPh₃)₂, up to its first oxidation product; b) 1-Ir(PPh₃)₂,starting after its first oxidation product is formed; and c) 1-Ir(py)₂.FIG. 21 is a graph of spectroelectrochemical results for a CH₂Cl₂solution of 1-Ir(PPh₃) at 1.0 V vs. Ag/AgCl; the inset is a graph of thespectra of the starting material (red), the first oxidation product(green), and the second oxidation product (blue). FIG. 22 is a graph ofspectroelectrochemical results for a CH₂Cl₂ solution of 1-Ir(PPh₃)containing 5 equivalents of PPh₃ at 1.0 V vs. Ag/AgCl; where thestarting material is red and the final product is purple. FIG. 23 is agraph of electron paramagnetic resonance (EPR) spectra taken at 20 K infrozen toluene solutions (with small amounts of CH₂Cl₂ to solvate t-4bpa for the top two spectra), of the chemically oxidized forms of(clockwise from top left): a) 1-Co(py)₂; b) 1-Rh(py)₂; and c) 1-(py)₂;where the blue traces are the experimental spectra and the black tracesare simulations performed using the SPINCOUNT package. FIG. 24 is agraph of a 300 MHz ¹H NMR spectrum of 1-Ir(py)₂. FIG. 25 is a graph of a300 MHz ¹⁹F NMR spectrum of 1-Ir(py)₂. FIG. 26 is a graph of anelectrospray ionization mass spectrometry (ESI-MS) trace for 1-Ir(py)₂.FIG. 27 is a graph of a 300 MHz ¹H NMR spectrum of 1-Ir(PPh₃). FIG. 28is a graph of a 300 MHz ¹⁹F NMR spectrum of 1-Ir(PPh₃). FIG. 29 is agraph of an ESI-MS trace for 1-Ir(PPh₃). FIG. 30 is a graph illustratingchanges to the electronic absorption spectrum of 1-Co(PPh₃) in CH₂Cl₂upon addition of excess PPh₃. FIG. 31 is a graph illustrating changes tothe electronic absorption spectrum of 1-Co(PPh₃) in CH₂Cl₂ upon reactionwith iodine. FIG. 32 is a graph illustrating changes to the electronicabsorption spectrum of 1-Rh(PPh₃) in CH₂Cl₂ upon reaction with iodine.FIG. 33 is a graph illustrating changes to the electronic absorptionspectrum of 1-Ir(PPh₃) in CH₂Cl₂ upon reaction with iodine. FIG. 34 is agraph of the electronic absorption spectrum of 1-Co(py)₂ in 5%pyridine/CH₂Cl₂. FIG. 35 is a graph of the electronic absorptionspectrum of 1-Ir(PPh₃) in 5% pyridine/CH₂Cl₂, illustrating that1-Ir(PPh₃) is not converted to 1-Ir(py)₂ under these conditions. FIG. 36is a graph of an EPR spectrum of singly oxidized 1-Co(PPh₃), taken at 20K in frozen toluene. FIG. 37 is a graph of an EPR spectrum of singlyoxidized 1-Rh(PPh₃), taken at 20 K in frozen toluene. FIG. 38 is anillustration of the atom numbering scheme used in electronic structurecalculations for compounds according to embodiments of the presentinvention; hydrogen atoms are in white, carbon atoms are in grey,nitrogen atoms are in blue, fluorine atoms are in green, and the metalis in lighter blue; note that the numbering of the corrole ring isdifferent from the numbering convention of molecular nomenclature. FIG.39 is an illustration of the molecular orbital (MO) surfaces(isovalue=−0.05) calculated for (tpfc)M(NH₃)₂, where M=Rh (left; Coshows similar results) and Ir (right); the topmost MO is the HOMO, whichis followed by HOMO-1, and so on, until the MO above 1a, is reached; 1a₁is HOMO-13 when M=Rh, HOMO-14 when M=Co, and HOMO-4 when M=Ir. FIG. 40is an illustration of the relative energies and spin density surfaces(isovalue=−0.002) calculated for [(tpfc)M(NH₃)₂]⁺ (M=Co, Rh, Ir). FIG.41 is an illustration of the relative energies and spin density surfaces(isovalue=−0.002) calculated for [(tfc)M(NH₃)₂]⁺ (M=Co, Rh, Ir). FIG. 42is an illustration of orbital drawings and energies for [(tfc)Co(NH₃)₂]⁺and [(tpfc)Co(NH₃)₂]⁺. FIG. 43 is an illustration of orbital drawingsand energies for [(tfc)Rh(NH₃)₂]⁺ and [(tpfc)Rh(NH₃)₂]⁺. FIG. 44 is anillustration of orbital drawings and energies for [(tfc)Ir(NH₃)₂]⁺ and[(tpfc)Ir(NH₃)₂]⁺. FIG. 45 is a graph of a ¹H NMR spectrum of a platinumcontaining metallocorrole according to embodiments of the presentinvention. FIG. 46 is a graph of a correlation spectroscopy (COSY) ¹HNMR spectrum of a platinum containing metallocorrole according toembodiments of the present invention.

Metallocorrole complexes of third row transition metals may be used astherapeutic agents, catalysts, components of oxygen detectors, andcomponents of light emitting diodes. In particular, metallocorrolecomplexes of third row transition metals may be used improvedphotosenitizers in photodynamic therapy; as improved catalysts inaziridination, epoxidation, and water splitting reactions; as improvedin vivo imaging agents; and as improved components in the emissive layerof OLEDs. Due to their strongly sigma-donating nature, corroles are ableto stabilize third row transition metals in high oxidation andcoordination states. Third row transition metals may be significantlymore electropositive than first and second transition metals and maytherefore act as improved catalysts. In addition, the high spin-orbitcouplings of third row transition metals couplings of third rowtransition metals lead to easier singlet-triplet inter-system crossingin the excited state, which in turn allows for long-wavelengthphosphorescence that is desirable for many applications.

While the present invention has been illustrated and described withreference to certain exemplary embodiments, those of ordinary skill inthe art will understand that various modifications and changes may bemade to the described embodiments without departing from the spirit andscope of the present invention, as defined in the following claims.

What is claimed is:
 1. A compound comprising a metallocorrole of FormulaI,

wherein: M is Ir; each of R₁ through R₃ is independently selected fromthe group consisting of substituted and unsubstituted aryl; each of X₁through X₈ is independently selected from the group consisting of Hand-halo; and each of L₁ and L₂ is independently selected from the groupconsisting of binding sites and axial ligands selected from the groupconsisting of triphenylphosphine, trimethylamine, pyridine,4-methoxypyridine, 4-cyanopyridine, 3,5-dichloropyridine, and3,5-bis-trifluoromethylpyridine.
 2. The compound of claim 1, whereineach of X₁ through X₈ is independently selected from the groupconsisting of H, F, Cl, and Br.
 3. The compound of claim 1, wherein eachof R₁ through R₃ is independently selected from the group consisting ofphenyl, methylphenyl, 4-aminophenyl, dichlorophenyl, 2,6-dichlorophenyl,2,6-difluorophenyl, pentafluorophenyl, 4-methoxyphenyl,2,5-dimethoxyphenyl, 4-methoxy-2,3,5,6-tetrafluorophenyl,4-(pyrid-2-yl)-2,3,5,6-tetrafluorophenyl, and4-(N-methyl-pyrid-2-ylium)-2,3,5,6-tetrafluorophenyl.
 4. The compound ofclaim 1, wherein the metallocorrole of Formula I is selected from thegroup consisting of: 5,10,15-triphenylcorrolato M;5,10,15-tris(4-nitrophenyl) corrolato M;5,10,15-tris(2-nitrophenyl)corrolato M;5,10,15-tris(3-nitrophenyl)corrolato M;5,10,15-tris(4-bromophenyl)corrolato M;5,10,15-tris(3-bromophenyl)corrolato M;5,10,15-tris(2-chlorophenyl)corrolato M;5,10,15-tris(4-methylphenyl)corrolato M;5,10,15-tris(4-methoxyphenyl)corrolato M;5,10,15-tris(2,5-dimethoxyphenyl) corrolato M;5,10,15-tris(pentafluorophenyl)corrolato M;2,3,7,8,12,13,17,18-octabromo-5,10,15-triphenylcorrolato M; and2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(4-nitrophenyl)corrolato M. 5.The compound of claim 1, wherein the metallocorrole of Formula I is5,10,15-tris(pentafluorophenyl)corrolato M.
 6. The compound of claim 1,wherein the metallocorrole of Formula I is2,3,7,8,12,13,17,18-octabromo-5,10,15-tris(pentafluorophenyl)corrolatoM.
 7. The compound of claim 1, wherein the metallocorrole of Formula Iis selected from the group consisting of5,10,15-tris(pentafluorophenyl)corrolato iridium(III) (trimethylamine)₂,2,3,7,8,12,13,17,18-octabromo-5,10,15- tris(pentafluorophenyl) corrolatoiridium(III) (trimethylamine)₂, 5,10,15-tris(pentafluorophenyl)corrolatoiridium(III) (4-methoxypyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III) (pyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III)(4-cyanopyridine)₂, 5,10,15-tris(pentafluorophenyl)corrolatoiridium(III) (3,5-dichloropyridine)₂,5,10,15-tris(pentafluorophenyl)corrolato iridium(III)(3,5-bis-trifluoromethylpyridine)₂, and5,10,15-tris(pentafluorophenyl)corrolato iridium(III)(triphenylphosphine)₂.